"someone sells a set of plastic clip-like protectors that slip on the rim"
I just cut up some strips from heavy plastic orange juice jugs and it seemed to work okay. Any thick plastic would work. I like the zip tie idea.
the beauty of the plastic clips is that they are shaped like the rim and actually clip on, so they stay in place pretty well, plus you can slide them around the rim as needed (though that in itself would probably scratch painted rims)