You will find that if you leave the plugs in then this will help a lot, as a few sharp taps of the hammer on the ratchet handle will soon shake things loose, try to turn the ratchet across the flywheel, ie so it is somewhere over the face of the flywheel instead of out side pointing towards it as there is then less of a lever effect trying to rotate the flywheel.
If not I have jammed a rag in the bottom pulley/fan belt before now to help and it works to stop rotation.
Of course if you have an air gun all the better.
tabetha