Hi 1jz,
Here in Canada the references are given by CAR 705.40 and its applicable standard 725.40. That's for the airline side, although the Commuter Regs are identical. You must be approved by Transport Canada to refuel with passengers on board.
In our COM we have a whack of different considerations when fuelling with passengers on board, but the big ones are that at least one crew member (pilot or flight attendant) must be on board, the main cabin door must be unlocked and open during the summer or unlocked and cracked open during the winter, there must be direct communication with the refueller (with is considered either via a headset or by hand signals through a window), the passengers must be seated or in the process of being seated and must not have any headphones on. The seatbelt sign shall be off and any emergency exits that take passengers away from the refuelling side shall be armed (if applicable).
At no point, however, does it state that the crew member must be in the flight deck. The intention of having the crew member on board with passengers during refuelling is to initiate and manage any evacuation should one be required, not to monitor the fuel load. At least, that is our rationale.