Had my 944 broken into last christmas through the same window. Here it is from the link posted above.
1. Install the rear window glass by wrapping a piece of heavy string around three sides of the window inside the groove of the rubber trim piece (top, front, and bottom side but not the back side).
2. Insert the back edge of the glass into the window opening with the groove of the rubber trim piece on the lip of the window opening (ends of the string on the inside of the car).
3. While holding the glass against the outside of the car, start pulling one end of the string from inside the car. This will pull the rubber trim piece over the lip of the window opening.