September 29, 2020
it took me a while to understand you mean a "new wall" as I was looking into the project context menu to see how to "add a surface".
Your tip only works if there aren't any cabinet into the "project". Not yet I put the a cabinet in front of the outlet made with a "surface", it disappears (as it is behind).
To check if any opening done in the cabinet carcass correspond to the outlet (electrical ones should be very well aligned), the only workaround I found is to make the main wall (where the outlet is located) AND the "outlet" surface 100% transparent. Turning the project 3D view on the back side the outlet outline shows up, and you can roughly check the alignment.
Anyway thanks for the suggestion and take this as an area for future improvements.
January 20, 2017
Maybe a Surface with texture can be a solution for you?
Click on this link for a video Support>Polyboard videos>Project mode>Adding images to your project