In principle you can do this with a piece of PET film such as Mylar (tm) -- see
http://en.wikipedia.org/wiki/PET_film_( ... _oriented) . If cut to the exact dimensions, with the proper back finish it should stick to the screen just by static attraction. The hardest part of the project is probably getting a small, clean piece of clear Mylar without having to buy a whole roll, cutting it to exact dimensions -- obviously you don't want to run an Exacto knife over the edge of your screen, and avoiding creases in handling. If you don't mind disassembling the bezel dimensions are not so critical, it could be cut slightly over size. You also probably want to choose a thin piece of film, since the existing screen already tends to touch and rub on the trackpoint, and to minimize reflections between the inner and outer surfaces. Obviously, when applying it the screen has to be absolutely clean and the application must be done carefully to avoid any bubbles; because the Mylar has a certain rigidity it should be easier to avoid bubbles than with a more floppy plastic film.
Still, I don't quite think it is worth the effort.