I hate the rope solution Joe, but I know you have a lot of experience with it, and it works for you. Because the con rod is in compression, I think it is less likely to break than the piston crown.
Another ugly solution that is likely to work, is clamping the blade plate to the mower base, then using a socket on the flywheel nut. The reason it is ugly, is the crankshaft is taking a lot more torque than it should have to. I think it would be stronger than the piston and rod, at least.
