24mm socket on a breaker bar. With the socket on the bolt head, rest the handle against the motor mount. Crank the engine BRIEFLY or pull the plug wires. Worked well for me.
I found this tip on the web somewhere and my 500lb-ft impact gun wasn't doing the trick.

Using the starter is not something I'd normally suggest due to the amount of force and how the breaker bar/socket can become airborne and cause harm/damage. Recaping..more than 300ft lbs of force at the speed of the starter can cause the socket/bar to fly off and hurt the person holding it..or damage the car/things around the car...you simply can't be sure what might happen.

If I wanted to stop our engines from starting...I'd unplug the ICM connection. If you undo the plug wires..you'll still have that high voltage grounding somewhere.

I agree 100% that using the starter sounds less than safe and had to think about the consequences for awhile before deciding to proceed. With the socket engaged to the bolt, I turned the hb cw (by hand) until the handle was tucked into the motor mount so it wouldn't start flying on its own. After bumping the starter, I found the handle had not moved at all, was still tucked in the motor mount and engaged to the bolt which had now been backed out about 3/4". It worked so well (not to mention easy for a change) I felt it was worth passing on.

p.*. I did not have anyone holding the handle and it would be a very bad idea indeed.

I did exactly what you did and works fine. But Torquing it back on I used a weighting lifing bar and a 4 foot extention with a 3/4" Ratchet and socket for Fleet trucks.