In the VideoHelp list of DVD players,
http://www.videohelp.com/dvdplayers
Look for the "MPEGISO" feature. Players with this feature can play a .MPG file in a data disc.
I have a Philco player that can handle this, and a JVC that can't.
But note that with a .MPG file in a CD/DVD data disc, even if your player can play it, you'll problably lose all navigation resources like chapters, angles, ff and rw, etc. You'll problably also lose subtitles, multiple languages etc. You may also experience some problems with aspect ratio.