A moving clip would be more difficult, as you would need to manually animate a mask (rotoscope) for the silhouettes. It may be possible to do automatically if you could find a scene from a MST3K DVD where the actual movie is mostly white and the only black parts are the shadows.

But I suggest you try the still image approach first until you get the hang of the technique. Either add a subpicture with your DVD authoring software, as adywan suggests, or use AviSynth to overlay the image and re-encode the video.