in a pickle any machinists?

So I broke a valve cover bolt off in the head. So I went out and bought a screw extractor and followed the instructions. But.... now I have a broken screw extractor. its down below the head so cant weld to it. Ive tried... using a chisel to break it up no luck. Anyone got any ideas? Thinking about a carbide burr but hate to spend the money if it dont work.