i'd try cutting a slot in the head with a dremel tool or die-grinder and use an impact wrench (the kind you smack with a hammer) to get them out. you could also try using just the tip of the impact wrench on a pnuematic impact wrench (mine pulls off and takes a 3/8's ratchet). that way you could push hard and let the impact wrench do the work. they should come out pretty easily.