--"The only option I can think of short of drilling holes is to remove the mounting screws that hold the motor and regulator in place"
Well, if you can get to the screws / bolts that are holding the motor in, go ahead and pull it. Go to rockauto.com and look up window motors for your vehicle. They have some photos you can look at. Looks to me like the motor drive end will just pull out once you undo the mounting bolts.
Then you can manually try to jiggle / wiggle / cuss / the regulator assembly into moving. The right combination of cuss words can often be very effective.
