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Here's a Q&D example of what I think you're talking about. I did it in a few seconds in Photoshop–two copies of the pic on separate layers, and simply scaled the top layer down.
You'll need to lock your camera down, and shoot your actor pretty close to it. Get a second or two of the scene with no one init before the actor steps in to his mark. Frame grab the empty shot, scale it down, and superimpose it. The shot should sell, so long as the actor doesn't step into the portion of the fram with the frame grab superimposed.