The only way I could think of is to script the box so that when a trigger is active (controlling_box=true) then the box responds to key strokes like a scripted player. The only thing wrong with that would be when you throw the box RF's current lack of physics wouldn't be very helpful.
that should be possible
I would add a PlayerDistOrder, then when the player is in a certain range to the pawn, the script would check for keys being pressed and move the pawn accordingly