Actually,
Flight Attendants can jumpseat in the cockpit jumpseat, if their airline's operations manual allows it. I used to be a dispatcher at an airline that did allow this, and I put them on the jumpseat regularly. Actually, just about anyone can get approval from the Director of Operations, but those that are not certificated airmen must have a seat avaiable in the back. So, it doesn't help to get you on a full aircraft.