an easy out can be bought at sears or most any tool store, including homedepot and lowes. they are use for stripped screws and roulded bolts, it is similar to a drill bit, except the flutes are designed to dig into the metal and hold not remove the metal in small shavings like a drill bit. You'll drill a small hole as if you would for taping a hole in metal, and then insert the easy out. the easy out is reverse threaded so you will "thread" it in counter-clockwise. as it gets tighter and deeper it is tuning the screw in the direction to loosen it.

http://www.sears.com/sr/javasr/searc...=searchresults

the top one should do what you need, check homedepot or lowes for price comparison.