This is the response I received from my dealer re the 996 collapsable spare option for the 997:

"Even though the 996 space saver might physically fit it is doubtful that it would be safe.

The 996 had a maximum wheel size of 18", whereas the 997 C2 S has 19" wheels as standard. The overall diameters and the rolling radius of the wheel/tyre assemblies are different on a 996 than a 997, which might make the car unstable and cause problems with the cars electronic systems.

We would not therefore be able to confirm that it is safe to do this and should you choose to do so it would be entirely at your own risk, both to your safety and to the reliability of the car.

However, in some markets Porsche are still required to provide a space saver spare and it should be possible for us to obtain the parts for a 997 C2 S if desired.

An initial investigation indicates that the parts required are as follows:

Emergency Wheel @ Pounds432.84 + vat
Boot For Emergency Wheel @ Pounds196.00 + vat
Scissors Type Jack @ Pounds81.34 + vat
Foam Part @ Pounds21.03 + vat
Threaded Bolt for Assembly Wheel @ Pounds3.79 + vat"



This fits on top of one of the rear seats - I've seen a picture somewhere - looks like a large black bag sitting on a polystyrene foam moulding restrained by the seat belt.