Is it possible to reach an A340's fuselage from the ground?
Yes, the refuel/defuel service panel can be reached from a person standing on the ground.

From the Airbus A340-200/-300 Aircraft Characteristics - Airport and Maintenance Planning document, the height of the panel in question is just under 2 meters from the ground:



The panel is located on the lower area of the wing/body interface fairing as seen here (item 13):