[Jamesp]

Cut a slot into the protruding bolt with a dremel tool and a cutting disc. Use a flat blade screwdriver to remove the screw. If that fails drill the center through with a tiny drill bit 1/8 or less. Being off center a little bit is a benefit. Continue with larger bits until you're cutting into the threads on one side a little. Use a cold chisel and hammer to strike the protruding part of the bolt in the direction you wish the screw to turn. If all fails at that point then use the easy out. Easy outs can work, but if you snap one off in a drill hole you have a bigger problem.

Penetrating oil over night or longer also can be a life saver.