Yep.
Grab the dog by the collar and start toward the tail gate, say "load up" as you lift the dog by the collar enough to clear his head and neck, dragging the rest of him over the tail gate. Be consistent with it and before long you will only have to touch his collar and say load up, later you will only have to say load up, later he will be reading your mind.
Yep, this is what we do and seems to work fine.