How about breaking the nut free while the chain is on, the bike is in gear and pressing on the rear brake? That's how I did it and how I'll do it before the rally. Since you don't use a front toothed sprocket(think belt drive and pulleys), you didn't need to worry about bending a tooth or two on the front sprocket. That would be my concern-->Bending (waving) one of the front sprocket's teeth. Also the swingarm has the rubber chain guard on it. Might squash that a bit too.
I tried the wood block, but all I got was chunked wood...
