What method would be good to use on keeping a wheel on its music wire (.047 in this case) landing gear? All the wheel collars that I've seen only fit standard large diameter axles, and are way over size and scale.

Also, what can be done about keeping the inside hub from dragging on the 90 degree bend?

A small washer (a washer with a .047 hole?) could be soldered close to the bend, but the plastic hubs prevent any soldering after they are put on, so that leaves out a soldered washer on the outside in place of a collar.