As far as I know, you need to remove the seat ( and belts) which makes no sense, but neither do most rules! If there is no warm body in the passengers seat, then what realistic reason is there to remove the seat/belts? Hang on.......maybe in case of an accident, when the seatbelt buckle takes out your eye, and the seat breaks loose and breaks every other bone in the drivers body while you endlessly rollover....but then again if you buckle the passenger belt while solo it should hold everything in? Oh, never thought about cheating....maybe if you leave the seat in, you can pick up a navvy in a secret location which will give you an unfair advantage overall? Then again, you would need two seat belt cutters if you leave the. Seats/ belts in.
Damn Jonesy opened a can of worms with that one. I do like the secret nav comment. Maybe they will have us cover our seat belt clips in marshmallows. Don't reckon I go fast enough to endlessly roll it over but did have a crack last year with one little roll, probably why my wife is now cheering from the sideline.
Just a thought, maybe CAMS has this rule right. Put yourself in the shoes of a volunteer recovery person attending a very major mishap, there's the driver but he's in a two seater, he doesn't know every car & its occupants situations so lets then best assume there is someone wandering the track away from the car, the resulting search, albeit not required, could cause havoc. Just remove the seat & accept the rules.