Fantastic tip and I will certainly keep this in mind! I tried rocking with a 2x4 and 2x8 last night, and all I succeeded in doing was digging a 1 foot hole with the board - ground was a little wet too thoughI have had good luck pulling the head, poring oil on top of the pistons and let it sit for an hour or so. Then using a block of wood and a hammer to drive down on the piston that is highest. Usually will break free with little effort.
Once free, I rotate the engine through several times and soak up any remaining oil off of the cylinder before going back together.
This is the quickest way I know even though it requires some wrenching.