I've done this in the past using other tools to "pre-process" a video on my Mac but this might be a nice option for ffmpegX:

In the "Options" tab, let's add a checkbox to "underscan". This would have the effect of adding some black pixels to both sides and top/bottom of the video. How many pixels? 10-20? Just enough to permit the entire video to appear without being cut off by the overscanning of "normal" TV sets.

I've done this sort of thing using one of the TMPGenc tools (probably DVD Author) but, as I don't burn discs any more (only TV via H264 for iPod for me), I thought this idea worth mentioning.