Hi McPhearson,
What you could do is store the position of the motioncontroller in a transform variable at the moment you pull the trigger (because it probably will be difficult to just get the relative position of the controller to the box, the box is not a child of the player i assume).
Next you can get the local position of the motioncontroller to the stored point with a ‘convert transform to relative’ node, which outputs a vector you can use for your movement input.
Hope that helps!