About the VirtualDub Plugin: there is already a plugin that pulls the subtitles in "standard" SubRip files (.sub and .idx) from video files. I haven't tested it (a friend says it only works with VirtualDub 1.5.4) and I don't know how well it deals with tough cases like white subs on white background (it seems rather simplistic, from the interface), but it may be worthwhile talking to its developer about your request:
http://www.sharemation.com/PodPis/PodPis.html