I've sometimes had luck "locking" the piston by pumping glow fuel into the chamber, typically via the exhaust port or by removing the glow plug. If the latter, you must replace the plug. The liquid will prevent the piston from moving past TDC. You should then beable to break the prop free from the drive hub as the hub won't want to turn anymore. The liquid can also be easily poured out the exhaust port once done removing the prop. I've never had any issue from this method and I would assume this is an acceptable practice as I have seen tools that screw into the glow plug port that cause an interference fit preventing the piston to pass TDC. Cheers.