Broken water pump bolt removal

I snapped that same bolt off once and it snapped off flush with the block.

That is what I think mine has done as well by looking at what remains of the bolt. It has about an 1/8" of the thread still on the bolt. I'll have to see if I can find a ride into town to get me acetone and I'll try the acetone/ATF mix and some left handed bits. Thanks for the ideas and input.