Wow, I love the originality of this idea but boy what a risk. I realize that the engine is just barely stuck as it hasn't sat like this for very long, but boy what if all that hydraulic pressure were to crack the piston or a ring? Seems like a lot of risk. But I do believe that more often than not it would work. Once you have the engine freed up using this method, I would imagine you fire it up with that spark plug out to get the cylinder cleared, then put the plug back in? How long does it miss on this cylinder before firing again?
I would love to watch someone use this method, but I think I would be much more comfortable if it wasn't on my tractor.
I really do think its a neat idea though, just risky.