Manual or Auto?

Manual, put it in gear (5th would be nice) and set the parking brake. If that is not enough, put it in 4wd, in gear, set the brake and have someone stand on them too.

Auto, well...you could drop some cotton rope in a spark plug hole and then rotate the engine. The rope will prevent the piston from coming all the way up, effectively locking the crank in place.

All in all, 123ft-lb is really not that tight.

Michael