You can't do that with LCDs. CRTs could do that because you could adjust the area of the screen where the electron guns that produced the image were pointed. LCDs work in a completely different way. You have little strips of liquid crystal that changes colors when you do specific things to it.

I have seen a few LCD monitors that allow something like what you want, but never a laptop display. With any luck, someone else may have better news for you.

One thing I can suggest, is tinkering with the aspect ratio of any movies you play back. If your laptop is widescreen (16:9 usually) and your projector is letterbox (4:3), then if you adjust the output of the video to 4:3, it should help. It just may sort of "squash" a widescreen formatted movie.