Thanks, INDY!!
I have a friend with a lathe. I'll ask him to machine down a wrench. I like the S1 wheel idea as well. For now, I have a 5mm washer between the wheel and the nut and that allows me (just barely) to tighten the nut enough.
Back in the day, HPI made 5-spoke wheels for trucks that came with a set of plastic universal adapters. They also came with an aluminum washer to put between the nut and the wheel. Wish I could find a couple of sets of those again.
Scott