For the sake of quickness, I used a magic wand mask tool to select out the canvas areas. I used these masks to clip each of the paintings to appear they were actually part of the canvases. This effect was sufficient to product the illusion for the final project at work. When I got home, however, I decided to do it a bit better and traced the outlines of the canvases using a path tool rather than relying on the sloppiness of the magic wand. As a finishing touch I overlaid the "painted canvases" with a multiplied gradient fill to match the varied lighting on the wall.
Now I'm wishing there was a way to convert the fake paintings in this image to real ones, because they would make an interesting and colorful decoration!