FrameServe out of Vegas4 with debugmode.com 's free Frame Server (AV).
Then you can use the standalone MainConcept MPEG-2 encoder (you buy that, so you need to decide if it is cheaper to upgrade to V5 or V6).
If your source is DV, then you'll probably deliver YUY2 (YUV packed) pixels into MainConcept instead of RGB. I'll be corrected on that if anyone wants to jump in....
debugmode supports winding up and down your timeline so 2-pass isn't a problem.
BJ_M was the first one to tell us about doing this. Although he is probably using Vegas5 right now, with the included 2-pass encoder (related to the standalone code as I recall).