Chad,

Looking at the picture of your wheels bought to mind a technique I used for making scale wheel retainers for my T/F 1/5 scale Mustang.

To make the retainer I went to the local hardware store and found some of those drive on cap nuts like are used to retain wagon wheels. Found one of the approximate inside diameter to accept a 3/16 wheel collar. The collar had to be filed down a little to fit, and once in place I ran solder around the inside to secure the two. I then drilled a hole on the outside large enough to fit the set screw through to the wheel collar.

When looking at it compared to full scale pics it looks dead on.