Okay that's good news. I guess the tech may not have understood my question or just didn't know what he was talking about. Thanks Karyn.

Level automation by ear to get the different lines "even."   Then a comp - the Cake optical is my favorite for leveling and adding some tone.  The standard 1176 will also work for that, although I use it more for an "on/off" switch.
 
If the tone still ain't right, start laying an EQ on the tracks.  The Blue Tubes stuff, as said above, is great for adding some steady state tone on top of tracks.  Since it is an older plug, the tone it has doesn't seem get heavier when driven.  It should work well for your needs, dissolving the small changes in tone between takes under the BT sheen.
 
 
 

Getting levels right is easier.  I would monitor rms levels with a VU meter over every vocal phrase and check that phrases nicely meet the reference level. 0 dB VU.  Note* The VU moves in one of the nicest ways possible with well sung vocals. Add or subtract gain as necessary on phrases so they all meet 0 dB VU nicely.  Bounce a level perfect track.
 
Do this before any compression takes place for an even smoother outcome level wise.  Once you get a vocal track leveled this well by the way it makes no difference what compressor you use after this. Because mild compression setting is all it takes for a nice conditioned vocal take ready to go into your mix.  Almost any compressor can do the job.
 
The areas where the tone changes are more important.  What I  do in this situation is listen to the whole vocal take and identify the larger areas where the vocal tone is normal and good.  Then cut the other areas where any tone changes are bothersome. Add EQ into these sections only. Clip based fx. Level changes can be tweaked in these phrases as well easily with the EQ output gain etc..
 
You will be surprised at how well you can match the tone change areas back to the original. It is a bit of a test for your ears.  You need to be able to jump to good sounding original areas quickly. Then back to the tonal altered areas and slowly move your EQ around and you can often get a near perfect match.  Set up a small loop around a short section of good area followed by the area you are tweaking the eq. Let the loop play while you adjust the eq.
 
Bounce a new vocal take with level and eq changes involved.  Drag that into the session instead and process your vocal chain as normal from there.  Done well it will sound as if it was perfect all along.  If the vocal performances are good then it is well worth massaging them a bit to make them work properly.  But if you can get singers back in there and they are willing, it will more than likely happen a little faster.  The EQ exercise is well worth doing though even for practice sake when you can't get singers back ever.

Volume and tone.... 
 
As the studio engineer, your job is to coach the singers and pay attention to things such as position in the room, how far they are from the mic.... distance in inches from mouth to the mic, if there's a pop filter, if the lava lamp was on or off.....always be sure it's on, and even to how they are singing. If it's a bad day for them, it's your job to call it a day. Most singers will try to push on, but you should call it a day if they're not getting the singing right.
 
A singer, even an amateur, should be able to get the same tone and vibe from one day to the next. They should be able to do a take on Monday, and come back Wednesday and do a punch in that is essentially  the same and requires no EQ fix.   In other words it should sound like the same session and like it's one take.  This assumes that they are not sick and are properly warned up vocally. If they take a break and come back and stand a few inches off from the last session, that really should not be a factor.... I can see if they are 6 to 12 inches off, yeah, you can hear that. But again that goes back to how professional they are and how observant you as an engineer are.  I like to tell singers I work with to stay within an inch or so of the pop filter, and I set the pop filter where I want it... That keeps them in the area within an inch or two.  A pro will do that without needing to be coached and will pull back for those power notes. And... if they come back from a break and sound different....call it a day and reschedule another session if possible.

Using envelopes is one thing.... I use them to adjust the volume of tracks and of takes and to push certain words or pull others back.... but to rely on plugs as a substitute for poor engineering is not the way to go.  Get it right going in and your life will be so much easier.
 
If there is a noticeable difference in the tone from one session to the next, you need to find out what has changed and make the proper corrections. Doing a completely new take is an option if you can't figure it out. I have done that more than once with guitar tracks.... I don't often write down my settings and if I have worked on something else, the tone is subject to be really different. That's one of my shortcomings. But you're talking about vocals so that is a totally different topic. I've done vocal punches a week apart and couldn't tell the punch in after the fact.
 
Anyway, that's my 2 cents.

Sanderxpaner how do you go about sidechaining the vocal rider to the music bus ?

Getting things right at the source is always the preferred option.  Sometimes you just can't get the talent back though and you are stuck with what you have.  Good audio engineering often requires fixing less than perfect things.  Things can slip through the cracks especially when you are attempting to engineer and produce at the same time which does require extra skill.
 
My approach to fixing tonal changes is worth knowing so I feel it is a worthy exercise.  It has saved my butt a few times.
 
Things to watch out for when a singer goes off axis might be mids and high falling off slightly and the bottom end changing as well.  The good thing is that even if they go off axis they are still more than likely doing it under near optimum conditions such as a quiet studio, a reasonably dead area with little reflection and room sound around and a decent mic etc.. Applying EQ to some off axis phrases can work very well and in the final overall scheme of things it can be very hard to tell.
 
Just thinking other things I like to get 3 takes of everything.  One take alone is a bit dangerous. Chances they went off axis in the same spot on 3 takes is considerably less.  I edit phrases in from other takes regularly..
 
If they go way of axis like 3 feet away then you are in for a bit of fiddling.  It is possible to remove the room now more so (reverb removal tools) and it would require a bit of substantial EQ I would say.

I agree with you. Waves Vocal Rider works pretty well.  You can Write its fader moves to an automation lane and edit them further (e.g., to bring out softer words or syllables, etc.)
I've also used Waves MV2 which also provides some compression to allow raising the vocals level.
 
I highly recommend automating volume/gain BEFORE using compressors or other tools.  You want the compressor getting a fairly even signal.  Otherwise, you'll end up overcompressing portions of your vocals.

Kamikaze
Do you use a pop shield? As well as dealing with plosives, they are good for telling a singer where to be. They also remove the very close option, where you get a lot of variance in tone.

+1 This.

Renaissance Vox by Waves

northlake63
Sanderxpaner how do you go about sidechaining the vocal rider to the music bus ?

Create a send from your music bus, and select Vocal Rider Input 2 (I believe that's how the sidechain is labeled).