Surely the key does not directly operate a latch on yours, does it? I mean the way it does on an ordinary hatch, like on a Manta or Capri or Scirocco. It must still do something which pulls on the cables which open the jaws which release the hatch pins, unless you have a very different kind of hatch securing mechanism.
Mine is the normal equipment for a late car, certainly a late RHD car, as Olli indicates above. Is yours an LHD or pre 1989 model? If I remove the electric motor on mine, there is no way to open the hatch with or without the key except by crawling into the boot from inside the car and pulling the cables manually. If there is a recognised set of parts available to change from this unpleasant arrangement, possibly parts used by the RHD 968 CS, I am tempted to look into it. All I need is to find someone with a 968 CS so I can identify what parts I would need.
As I understand it, the 968 CS manual cable release can only be operated from inside the cabin: there is no external release at the back of the car and the keyhole and lock mechanism are removed and blanked off.