I had this situation a few days ago. The battery door of my ME Super was jammed beyond repair, i.e. the slit for the coin was severely damaged. I took off the bottom cover like you did, then took a copper coin and a mid-size soldering iron (50 Watts). Then I soldered the coin to the door and opened it. Alternatively, you may try to drill two tiny holes into the door and use a campus to open it.
The door thread was still intact and I took another door from a broken camera. It looks like Pentax battery doors from different models are interchangeable. I have also seen replacement doors on Ebay.
Originally posted by geauxpez Update: Took the bottom cover off this evening. There's no obvious leakage in the bottom workings...but even after freezing the baseplate and risking destroying the thing, the battery cover wouldn't budge.
My assessment of the camera: Rough. Brassing, scratches and bubbling paint. Jammed battery cover preventing testing the meter. Dirty but usable viewfinder. It desparately needs bumpers for the mirror. the good: the stupid thing works (or seems to). Low shutter speeds are low, high speeds are high and bulb works fine as does cable release. It's a mechanical camera -- what else do you need?!?! The leather is in surprisingly excellent condition, though it does smell like menthol cigarettes. The clencher: It's black. I just like black cameras. If it was silver, it would have been listed for sale last night.