Straightening bent rims

Lets say a friend of mine fell on the rocks and slightly dented the rim of
his cartridge reel so its out of round a little bit. Now, when he palms the
reel, instead of a smooth rub, he gets this pulsating because of the dent.
Its not enough to make the reel chirp, but its enough to be bothersome. Or
so he tells me. Are there any tricks for making the cartridge true again, so
it has that nice silky feeling it used to?

--riverman