I hooked up a wacom tablet into the computer, and set the photoshop image to fullscreen.
From here you can draw on the building 2 dimensionally.
You may note, that from the angle the photograph was taken, the illusion does not align 100%. This is because, though the projection will 'read' from many angles, it only matches up perfectly within a one foot distance from the projector. This does make moving around the 3 dimensional construction, while attempting to discern the 2 dimensional drawing a bit of a wild.
