32:9 Source streamed to 16:9 transform of source follows mouse side to side

[jdedmo]

So I am trying to find a way to link a sources position to where the mouse is at so when in a game which does not allow inventory or other UI to move into a 16:9 area, I can still stream what I am doing when on the edges.
I just cant seem to find info on how or where to start looking to find a way to.