Broke my water pump bolt. Now what? (Update - broken bolt is out)

Okay, many thanks all. Will try the least invasive procedures with hammering it a bit, heating it up and grabbing with a vice grips. If this doesn't work I'll escalate from there with the more involved procedures. In the mean time, I'm going to give it several days to soak up the PB Blaster and heat. I hope to report positive results in about a week. Thanks for the MANY excellent ideas - it's much appreciated!
Just a "heads up". You are only going to get one shot with using vise grips.
After you squat them hard enough to turn the bolt, if it slips, it will round out the bolt remains and make it even more difficult to try the other methods suggested.
The number one, tried and true method is welding a nut to the remains of the bolt. That is guaranteed success, even if you have to transport the engine somewhere to have it done. A portable welding truck would come to your house and do it for about 50-75.00 . (offer cash !! )