The airbag deactivation bar is the only way I know of, but you have to have a porsche child seat seatbelt to press into the buckle to actually deactivate the airbag. So once you get the bar you need to get the seatbelt to actually deactivate it.
There was a thread a while ago about how to make a seatbelt that will work so you don't have to buy the Porsche car seat.
