The easiest way would be to opt for the flight deck refueling panel (option for Airbus). Set it up and the bowser just needs to connect and go. On the A320 comes with fueling ports on both wings.
the only time i had to take an engineer along was when the MEL required a drip stick check each time, apart from that any pilot should be competent enough to handle it themselves. Even though the refueller is perfectly able to, just depends on the booked and paid for service level.