Is there any way to loosen the compressor and swing or slide it out of the way without opening the A/C lines? When I talked to my mechanic friend, I mentioned that it had A/C. He didn't mention anything special that needed to be done as a result to get at the pump, but maybe his information was incomplete. But I would think that if the quote you got involved work on the A/C as well that it would have been a much more expensive quote (due to the need for vacuuming out the lines, leak checking, filling with freon, etc.)

Leakage at the hole in the casting means that the shaft bearing and/or bearing seal is leaking. There's no way to fix that leak without removing the pump (plugging the hole will only cause coolant to leak out around the shaft). Removing the thermostat might lessen the pressure at the pump and reduce the leakage slightly, but it'll have other complications (the engine not getting to proper temperature, risk of overheating, etc.). I wouldn't recommend it unless you're desperate. Dumping StopLeak into it isn't something I'd recommend either. :-/

Does the A/C work? Would it be a great loss if it was disabled as a result of your work on the water pump?

I think you'll have to bite the bullet, or put this one down and get another steed.

Luck!

Cheers,
Scott.