Now I just need to hit the tires with some Armor All!
I expect I'll trim the rims with an inch margin of plasti-dip so there's no border visible at all around the covers. They are also still shifting a bit. The added grip from the trim would probably take care of it, too. But if not, I'll go ahead with pegging them to the center cap. The hole plugs are iffy on being easily removed by hand so I might end up popping a small hole in them for a hook to insert.
The low profile zip ties worked out really well. I put small pieces of electrical tape under them where they pass out of the hole so they wouldn't rub on the rubber when tightening.
Overall, I am pleased with the results.