Another option is to record the guitar as you would a bass, and drag it to a MIDI track (before pitching it down). Use (as an example) SI bass for the MIDI (transpose down an octave). Then pitch down your guitar and blend. 
All the best.
 

MarioD

fjz
 
I've gotten ok results using this method with SONAR's transposition process (at least to my ears).  I recorded a clean DI signal with my guitar, selected the wave file, then clicked Process - Transpose.  I then checked the "Transpose Audio" box, dropped the amount to -12, and chose the "Radius Solo (Bass)" type.  I then ran it through a bass amp sim.  The process was pretty quick and sounded pretty good to me.  The other suggestions made here may get better results, but I have not tried them.
 
If you're interested in hearing an example of what I described, here's a link to a quick little blues guitar video I did with the bass done this way:
http://www.dailymotion.com/video/x4gwm79_little-blues-guitar-jam-in-g_music
 

I used to do the same thing until I purchased a used Squire P-Bass.  This guitar transposed down an octave does work.
 
PS - great blues man!
 

Yes indeed... we do what we can with what we have.  Thanks for the kind words, MarioD!

As others have stated, the audio to MIDI convert option may be a good way to go here? Just record what you want using the electric guitar, then convert from audio to MIDI. Once in MIDI, you can use any VST for the bass? Works quite well...

A few things to consider:
 
1- there is no substituting a 4 stringed instrument. there are certain nuances between a VST Synth and a string.
the cycles are different and lets just say, not perfect on a bass. this gives it a real feel vs its fake friend the synth.
 
2-Bass guitars can be had cheap on craigslist or any second hand music shop.
a fender bronco can run you 75.00 used.
 
Im not opposed to using Synths at all, matter of fact I use them quite often to thicken my bass tracks.
On average I have 3 - 5 bass tracks.
track 1 - 4 string bass DI
track 2 - 4 string bass DI strategically placed to thicken up certain parts.
track 3 - Bass synth, yes absolutely SI Bass has some great sounds. but I use Kontakt Rick.
track 4 - almost a complete double of track 1 / watch for phase issues
track 5 - Octaves placed strategically to thicken parts (Bridges, Chorus)
 
I understand what your trying to do here, your looking for a quick fix.
that's understandable and I realize not everyone works like me (or works in the same ways)
but I find a real bass sound accompanied by a bass synth really brings out the power in the instrument that is going to define your musical piece. its the instrument that sets the rhythm section. its needs to be thick and bring out the low end without conflicting with the kick. this is why EQ is also important.
synths are great but almost too perfect and not real.
 unless of course you want that synth bass sound...and im just taking a guess but...if you DID want that "synth bass sound"
I don't think you would be here asking how to record a bass without a bass

I was really keen on amplesounds bass. I was looking at the complexities of the articulations available, and reading about how to program it so it sounds like a bassist played it. Then it dawned on me to look at how much they cost for real. I play flute and sax, and they teand to get expensive really quickly. When I found the price of a Squire Jazz Bass was about twice the price of the sample sets from Amplesound, I thought it was crazy to speand time learning to mimic a bass player, when I can spend that time learning the real thing. And being studio based, I can sit and work on getting 2 or 4 bars right, and not have to worry about the whole song live.
 
Its really changed my perspective on baselines and and openied up playing over chord progressions, instead of my previously modal approach.
 
I needed new speakers a while back, I was using cheap speakers waiting for documents to secure me in the county. I kept putting off my order for replacements from overseas. Then I saw an acoustic bass guitar in a shop here. Acoustic guitars are so common in Vietnam, you see bags strapped to riders backs everywhere, but not Acoustic basses. I've seen 3 in 2 years of being here. One is mine, the other a friend brought with him and the third in a shop in Saigon. I love it. Got my paperwork through, ordered 8" monitors, with some flats for the Jazz and Nylons for the acoustic. I'm kind of kicking myself for not doing this years ago, when I was around a friend who could have helped me learn a lot. I've not told him yet. I look forward to surprising him and get a masterclass when I next visit the UK
 

Kamikaze
I was really keen on amplesounds bass. I was looking at the complexities of the articulations available, and reading about how to program it so it sounds like a bassist played it. Then it dawned on me to look at how much they cost for real. I play flute and sax, and they teand to get expensive really quickly. When I found the price of a Squire Jazz Bass was about twice the price of the sample sets from Amplesound, I thought it was crazy to speand time learning to mimic a bass player, when I can spend that time learning the real thing. And being studio based, I can sit and work on getting 2 or 4 bars right, and not have to worry about the whole song live.
 
Its really changed my perspective on baselines and and openied up playing over chord progressions, instead of my previously modal approach.
 
I needed new speakers a while back, I was using cheap speakers waiting for documents to secure me in the county. I kept putting off my order for replacements from overseas. Then I saw an acoustic bass guitar in a shop here. Acoustic guitars are so common in Vietnam, you see bags strapped to riders backs everywhere, but not Acoustic basses. I've seen 3 in 2 years of being here. One is mine, the other a friend brought with him and the third in a shop in Saigon. I love it. Got my paperwork through, ordered 8" monitors, with some flats for the Jazz and Nylons for the acoustic. I'm kind of kicking myself for not doing this years ago, when I was around a friend who could have helped me learn a lot. I've not told him yet. I look forward to surprising him and get a masterclass when I next visit the UK
 

very cool man.
Im a lot like you. though I don't play the sax and flute ( wind instruments) but if I had to, I would use a synth .
but only because I don't have one.
However.. if I had the option, I would buy a real one and learn it like you did with the bass.
 
when ever possible I grab for a real instrument because even the mistakes give your songs character.
they give it that something extra that a synthesized instrument can not.
varying tones, wavering pitches, different cycles (even on the same notes). each note comes in at 5/10ths of a second different.
 
our music is a reflection of ourselves. when we begin to quantize everything, it strays away and becomes robotic from what we are truly trying to accomplish....
and thats an extension of the real reflection of ourselves.
 

Anderton

lowerfreq
Now if I could only program my brain to think like a bass player

Just remember that you're part of the rhythm section, not the melody section 

Don't tell that to the late great Chris Squire of Yes!

Ditto to Beepster's, Craig's and Chuck's, etc, comments. I didn't expect to enjoy this thread as much as I have so, thanks to everyone! ( A Christmas Carol comes to mind! LOL)
All are much cheaper solutions than a Fishman TriplePlay pickup for midi or ElectroHarmonix PitchFork pedal, or an octave baritone like a Bass VI (funny that the Beatles came to mind.....). I have 2 out of 3 of those, plus a Jazz bass and am really tempted to get the PitchFork...... oh well, it's only money....
 
    I was just thinking about the music I grew up with (I'm 67+1/2! LOL)having both an upright and electric or a flatwound P and 30" Dano for a very "picked" flavor. It's like someone once said "kick drums haven't sounded natural/normal, since the thirties!"   We have come to expect to hear enhanced/exciting sounds and that certainly seems born out by "all of us" (or least a lot! LOL) going ITB to get as many tracks as we can, to achieve that magical end point. Actually, I don't think there is one, but I just stop after a while!
 
Michael

If you have IK's Amplitube 3 or 4, you just need to use the Pitch Shifter pedal (with a bass amp sim....i.e Ampeg) and you have da BASS!! :))
 
 

 
 
 
 

I've done what I'm about to mention here often for various instruments and musical tools I've needed .
 
IMHO, One of the best things you can do for now is to use what you have on hand right now and  plant the seed in you mind that you are gonna pick up a Bass when you are best able to do so . That thought and desire can certainly cut some of the sting of currently not having one. Also, It can release you from the mindset of not having a Bass to knowing  that your bass in on the way  .Now you are only doing whatever workarounds you are doing now in your music as a temporary  fix ...
A large portion of doing music creatively with what you currently have involves playing a mental game with ones self  .
 
Other folks here have given you solid advice ...
Interestingly enough ,  all though I have and play Bass , I recently have made a move to where I'm playing extended range guitars . They seem to work well in the places and musical sections where I would normally have used and played Bass...
FWIW , the only real main diff between a regular guitar and an extended range guitar is the scale length of the guitar and the low end range the few extra strings bring to the table ...
As a temporary fix , if you happen to have and extra guitar or two laying around , you may want to put a heaver set of strings on it and tune it down ...
After a little truss rod adjustment and a few intonation tweaks , you may be good to go ...
 
I don't this guy even did any of that ... he is cooking
 
 
 
all the best ,
 
Kenny