Not that I am aware of, but I don't know everything. There may be some kind of frameserving way to do it but I havent read much about anyone doing that, probably because the results are good with the main concept transcoding from within Vegas. It is also realtime for rendered footage or straight avi's.

Check out the Vegas forum, they have a very good and knowledgeable group of people there who are very quick to answer, but search for your answer first, I'll just about guarantee that the ??? has been asked and answered.

Procoder
 

You can but The DVD architect doesn't seem to like the output file from Procoder. When I tried to author it it stated that it was incompatible "filename.mp2". I just use the mainconcept decoder built into vegas and it works just as well as procoder with the exception of the batch capabilities of Procoder. Also like you said you would have to render as AVI and then render again to MPEG-2. I hope you have lots of time on your hands ;p.

Vegas & DVDA don't like elementary stream MPEG files. Can you render it as an MPG file instead of an MP2?