Is it possible to make new heads in the screws by using a dremel and cutting a notch for a flat head screw driver? If so get a soldering gun and hold it on the screw head and let it heat the screw and melt the bedding compound around it. You should be able to at least get the screws out. This process will take awhile you just have to keep trying to loosen the screws until they finally break free.

Did you use any release agent at all or is the entire action now glued to the stock as well? Once you get the screws out you may have to carefully cut the stock off and replace it. Hope it all works out for you.