Jeff, short of mounting the film under a piece of anti-newton ring glass, which is itself slightly shimmed above the platen as Larry suggests, you could try some anti-newton ring spray. It puts a very thin layer of something on the platen, which is just enough to kill the rings without affecting the image in any detectable way.
This link on apug has some info on the Tetenal spray, and some interesting alternative solutions: (there was a url link here which no longer exists)