You don't have to remove the mirror housing from the car. Just use the motor to tilt the mirror to one side, or even all the way facing down.
"Then remove the plastic mount/holding plate by prying and pulling it off the pan/tilt mount. Note the wires for the defrosting pad that are attached to the plastic mount plate."
Proceed as above.
How do I know this? My story is a little different.
My driver's side mirror struck a lane divider where they were working on the road. It knocked the mirror assembly nearly flush with the door, the mirror-glass and plastic mount came loose and cracked the mirror. OK, shattered the mirror. I pulled over, the only thing holding the mirror-glass/plastic from falling off the car was a single heater wire. I connected the other lead and snapped the mirror assembly back on the pan/tilt mount.
Next step, I ordered the "Aspheric Mirror Upgrade" from Suncoast Parts
Suncoast Porsche Parts & Accessories Aspheric Mirror Upgrade
The new mirror was already attached to the base plate. So all I had to do was tilt the mirror down, gently pry off the mirror, detach heater leads, and reattach heater leads to new mirror.
Then I moved the mirror pan/tilt mount to a more centered position and snapped the new mirror in place. Took about 2 minutes for a project I thought would take a couple of hours.
I had a mirror like this in my old Saab 93. It's kind of like a low-tech blind-spot monitor.