A couple of things come to mind. Soaking them with wd 40 for a few days then using a 1/2 breaker bar try to tap them loose. Or run the engine for a while and before it starts too cool off use the lube and try to get them out before the engine cools. When the engine is hot the metal exxpands and trying to get them out before it cools around the threads and around the plug. There might be other answers to the problem but this is what I think would work.