For removing rusted stuff, I'll put a Liquid Wrench type of lube on it
once or twice a day for 3 or so days, then attack it. Tapping sometimes
helps, as does the application of heat (Careful not to catch the lube
on fire. A heat gun is better here than a torch). You might even get a
long-reach socket to fit--then you could use an impact driver, that'd
get it easy. As long as you didn't install the bit all the way into the
collet in the first place, you can use a hunk of wood to beat it down
once you loosen the collet (if the bit is rusted in place).

Just some ideas,
H.