There is a program called DVDSubEdit which is able to go into the copied VOB files on your hard drive (you'll need DVDDecrypter or DVDFab Decrypter for that), go into the VOB files and justify the placement of the subtitles. Unfortunately there isn't an option (yet) to downscale the size of the fonts, so the subtitles remain as large as they are now.
Go to http://www.videohelp.com/~DVDSubEdit/ for more info and to download the program.
Good luck