Hey Roland - On some early European cars with electric door locking circuits there was a procedure that allowed you to remove one of the tail light assemblies for access to the wiring. I had an old Merkur Scorpio that a paint and body man was able to touch a couple of wires and get into in about 5 minutes one time. I don't think the 928 can be tricked into unlocking it self by jumpering it's circuitry. Even the early models still shut like a vault with all the doors closed.
Just after buying my first 928 it came with an assortment of misc electrical issues including an intermittent door locking system. With both interior door panels removed while trying to determine how the circuits worked - I accidentally locked and slammed the driver's door with my only key laying in the seat. This naturally stopped my heart for a moment or two. Luckily the passenger's door was not completely closed so I was able to still get in.
I later had talked to two lock smiths about a potential 928 lock out emergency and neither was sure they could have gotten in without damaging something. After that close call I came up with a "Guaranteed - Sure Fire" method to prevent a similar accident. I had several duplicate keys made - gave one to the most reliable person I know - my wife
then hid one over the front splash guard and one stashed under the rear fender - both sealed tightly and stored in a doubled zip lock bag.
If I remember correctly, I had to send the original key off to a specialist for the duplicates to be made.
Good Luck, Michael