As Boxzilla said there is an airbag deactivation bar for 986s that needs to be installed under the passenger’s seat and then the car's computer needs to be programmed by a dealer to recognize the bar.
http://www.****************************************************.com/product/99680308302.html?Category_Code=986seat
The Porsche branded child seats have the matching buckle that fits into the receptacle on the bar and the airbag is turned off.
FYI: There is a (hard to find) pattern on the internet for reproducing the child seat side of the buckle that can be used with the deactivation bar to turn off the airbag w/o using a Porsche booster seat.