The brochure on the NHTSA website makes it sound like you do not need to deactivate the passenger side air bags as long as the child is at least 10 inches away from the air bags. If I've read this correctly, then the Porsche seat is not necessary as long as you move the seat back as far as it goes. If this is the case, then I'm pretty pissed at Porsche for making everyone think that they HAD to buy a special car seat!!!!
http://www.nhtsa.dot.gov/cars/testing/ncap/airbags/Brochure/index.html