When Nony & I did the Super Reaper that question came up, here is a pix. of the piece we made to fit on the wire axle. I made a similar one to facilitate mounting the brake to he replacement aluminum gear. They work great. Where the allen wrench is through I put a bolt and a nyloc nut through and can then do a bit of clamping and to hold the piece on if the wheel falls off, don't ask why that might be necessary.
Bart