When I read the title I was gonna be a smart-ass and tell you to use DVD Shrink. :laugh:
But now that I read it the only things I can think of are Overburn and resampling the videos.
I have no idea how overburn works with a DVD, you'll have to investigate that for yourself.
The other option is to recompress one of the videos and make it small enough to go on the DVD. Naturally you will lose some quality, and it seems to me that everytime I redid a video just to make it a little bit smaller (file size) it would totally fvck up the quality. Make sure you keep the original handy.