I tried pinning the fly wheel when I did mine and couldnt break it loose. I then got out my impact driver and used it, without locking up the fly wheel, and got the bolt out... it did take some time. My impact wrench isn't a real high torque model..... but it did work....eventually...

CAUTION: Be sure to place a piece of plywood or something against the radiator so you dont run the wrench into the radiator while backing the bolt out. I had a nice piece of 3/8" plexiglas and I backed right up against it with my wrench.... that would have been bad without the plexiglas..