The wingnut idea is flipping brilliant.

Might take some searching but I'm sure I can find a durable wingnut with the right threading. Doesn't have to be too strong. It's just holding back minimal lateral stress of the wheel. It's not supporting any weight at all.

Home Depot has a surprisingly deep assortment of little parts like that. I'm going to go pull the nuts off of it now (that didn't sound right) and go run over to Home Depot and see what I can match up.

Thanks, friend!

The converter idea is sound, but $20 per wheel....I only paid $60 for the bike. I bet I can make removing the wheels a simple task for $3 in wing nuts. I'm kind of embarrassed I didn't think of it myself.