I've got a Cabrio and took my "tailgate" apart - it was just 6 of 8 Torx screw and the plastic panel just separated (be careful to support the gate when taking off the last screw!). Anyway, on the inside surface of the plastic panel I found 2 nuts glued to the back side for holding the license plate (tags to us Floridians). One of them had been popped off by the over eager salesman at the dealership attaching the temperary tags, so I just hot-glued it back on.
The disassemby / assembly took all of 5 minutes, so you might want to check it out before you start punching holes in the plastic!