Based on my experience at SFO last month you have to go by the desk and there SHOULD be paperwork with your name on it in a kiosk nearby. Since it was my first time using Fastbreak I had to go to the desk and check in. Make sure you have all the account info filled out online before you go and you may get lucky.
We did what you wanted, jumping in a car and going, but had to go back in and go to the desk.