Couldn't find the Du-Bro threaded coupler another Boxster owner used to join the broken cable to a closed end audio audio connector, so I used a small Eye Bolt found at a hardware store. First I twisted the wires to regain the semblance of a single cable at the latch in the trunk & pinched the broken end with mini channel locks.
After applying a liberal amount of flux to the cable I soldered the cable in 3 spots starting an inch from the white plastic cable guide & released the channel locks. Next place the eye bolt over the latch post along with the manual release cable and slide the small metal fastener over the end of the post to its lock position.
Apply plenty of flux to the eye bolt and heat it with your soldering iron. It took a while, but finally the solder started attaching to the eye bolt. Using repeated applications of flux to the wire and the bolt a thick joint of solder eventually formed where the cable rested against the eye bolt.
Due to the lengthy soldering process the heat down the cable caused some of the individual wires to separate at my spot welds so I used a screwdriver to push the wires back together & soldered the cable solid again. The key fob release now works as well as the release button in the door sill beside the driver's seat.
Needless to say we must be very careful what we place in the shallow trunk. My cable broke because the plastic oil catch pan I placed in the trunk to hold various auto products slid toward the latch on a very steep hill. The gallon antifreeze container wedged against the trunk lid causing the release cable to be severed at the hook. A short piece of 2x4 will prevent that from happening again. .....