Ha, you can drive. I'm gonna sleep. And Jen says that you have to play by the rules: http://www.shotgunguide.com/

Specifically, rule number 4:

Early calls are strictly prohibited. All occupants of the vehicle (including the driver) must be outside of the building and directly on the way to the vehicle before shotgun may be called. Under no circumstances may a person call shotgun inside a building. For sake of simplicity, a garage is considered to be outside. Parking structures and detached garages are always considered as being outdoors, even if they are underground.