LOW TECH SOLUTION.................
Measure the distance betwwen the sides of the swingarm at the front of the rear wheel. Now go cut a piece of 2X4 that width, and place it between the wheel and the swingarm, acting as a block to the wheel turning, and set the rear brake. Now go apply torque to the nut; it'll come loose quite easily, you won't need an impact hammer, and you wont mar your wheels, or damage the tranny.
Sometimes, low tech is best.