My understanding was that they use the underground tanks for storage but then use the trucks to actually get the fuel into the airplane, so ideally, they would have a hose from the truck to the ground, and another hose from the truck to the airplane wing.
Logistically (not to mention within the coding... something I have no knowledge in), I am not quite sure how they would do this since it is supposed to work with every type of addon. Maybe GSX could identify the wingspan and height off the ground and then find a point to plug in the hose and then stick it under the wing. Then have that line run to the truck and then identify another place a certain amount of feet from the fuselage to "stick" the hose into?