I'm not a pilot, just a humble dispatcher. According to FARs, the pilot in command is not in command until he is actually piloting the airplane. Believe it or not, during the boarding process, the company can actually dictate who gets to ride in the back of their multi-million dollar machine. Imagine.

Of course, any captain can refuse to let an authorized person board. But not without answering for it, and he'd better have a damn good reason, and just saying "PIC" won't cut it.