The best way I have found to get them off without marring them is to remove wheel, take a rubber mallet handle (or something similar) and gently tap from the backside of the cap, while using your other hand to catch it on the front side. Or some variation of this, like lay them face down on a towel and do it, etc. I do the same with SSII/III Olds wheels, although since they have an edge, you can pop them off usually without taking the wheel off. But some are very stubborn. Avoid any pry tool.
PITA, but if you don't want f'd up caps...