Is this possible with Sonar (latest version)?
Just need to insert a ritard to drop tempo by maybe 30% for last couple of bars of a song.
 
It's probs been covered before but a quick search revealed not much...somehting about "Shift-M" and perhaps Melodyne?
 
Looking for  quick way to do this, not a task involving a "thousand swetaing clerks" hahaha, if you get my drift. Its one song, and its 4 bars, so if its not quick and easy, not sure I could be bothered

Tempo map?

Audio Snap so the audio can follow the tempo then like Dave said, tempo map.
Tricky stuff but you can do it.
Let us know how it goes.

You can draw them in the tempo map.  But I have had success experimenting with selecting the timeline and Project\Insert Series of Tempo which gives you this dialogue.  It is much smoother than trying to draw manually.
 
As others have said, you may need to use some Audiosnap functions if you have audio involved.  Here is a good video from our friend Karl Rose  X1 Creating a Tempo Map - doesn't cover creating a ritard but may help.
 

What Wren does above is what I have done in the past.  I couldn't remember the exact steps.

Thanks, but that is really about MIDI, I am doing audio

Yah but once you draw in the tempo ritard you can enable audiosnap and have it follow the changes. I prefer to do it in MIDI but it is possible with audio. You might have to split your clips right before the tempo changes so audiosnap is only working with the part that has changes. 
 
I usually get my arrangement all settled with MIDI and then insert small changes all over the place, like a tempo bump of 2bpm before a chorus and vice versa, so when I render the audio it's already built-in. 

...wicked
Yah but once you draw in the tempo ritard you can enable audiosnap and have it follow the changes. I prefer to do it in MIDI but it is possible with audio. You might have to split your clips right before the tempo changes so audiosnap is only working with the part that has changes. 
 
I usually get my arrangement all settled with MIDI and then insert small changes all over the place, like a tempo bump of 2bpm before a chorus and vice versa, so when I render the audio it's already built-in. 

Can you do this just for the specific tempo ramp section? Select a region for fade and have AudioSnap just apply to that vs. the whole project or track? Maybe you can already do that?

Let's say you recorded a series of songs at different tempos and wanted to insert a tempo gradation/ramp to another tempo and have the audio follow that? Or, the band plays along with a metronome/click track, but gets ahead or behind , just at a certain spot, but resolves back to the click. Is there a way to have just the audio at one, or several measures, "catch back up" or slow down to make it sound like they were still on the beat, just at that measure?

I had a session a while back, where the whole band stopped at a break, but rushed it (relative to the metronome/click track) and then caught up/re-resolved on the downbeat after the break. How would you fix something like that?