Creating an action to move layer to opposite side of canvas

I'm trying to create an action that will duplicate the background layer, double the size of the canvas, move the new layer to the opposite side of the canvas from the background layer, flatten it, and then save—essentially, to create an image with two of the original image side by side. Trouble is, the images I want to use the action on are all different sizes, and I can only figure out how to record moving the layer by the number of pixels it moved. So it'll only work on pictures the exact size of the one I use to create the action. Is there a way to record moving a layer to the opposite side of the canvas, regardless of size, instead of by the number of pixels moved? Thanks for your help.