[Christ]

Hubcaps are usually put on with a metal ring inside a semi-flexible plastic set of "teeth" or "fingers". The metal ring is split so that it's compressible, but holds to it's original form.

If you have access to a NAPA store, you can find some clips that hold plastic tabs for things like a-pillar trim and the like. You could JB weld those tabs on to the pizza pan or the rim and try to make them grip whichever side you didn't epoxy them to.

The pizza pan would be more likely the side to let them grip on, with the holders being epoxied to the wheel itself.

Another option would be to get some lugnuts with caps on them, and just drill small holes in the caps that would accept sheet metal screws. Put the screws through the pizza pan and into the caps of the lug nuts, and you don't have mounting issues anymore. Center everything up before you make the holes, though. Each hole should be 72* apart and I believe for the Toyota they should be 57 mm from center of the pizza pan.