I have never seen any other than rectangular screens, but I think you could pull it off with a rear projection technique using a Pico Projector.
Just project your image to the backside of a translucent white sheet of Vellum or similar plastic sheet. You will probably have to make a mask or cut a triangle out of a lens cap to avoid stray light, and only project onto the back of the screen, and may need some mirror experimentation.
Other options are buy 6 of those inexpensive 3.5" tft monitors, and stack them inverted pyramid, make a thick bezel, and use special 6 monitor video card.
Or if you have deep pockets have a pc board substrate made and stuffed with 0402 LED's in RGB matrix like those LED signs.
Cool and very ambitious project though, I loved that movie, and thought laying miles of a 4 lane highway as being a cinch, means I could have godlike powers with an Interocitor of my own. Make my own island 20 miles off the coast so I can start my own country, and invite only the worlds top minds to live there, provided they had the "Who Is John Galt" mentality.
I made a drive in theater screen out of an open frame LCD screen and laser cut framework for the Niles Depot Museum display of railroads next to drive in theaters. That was a project, so I can imagine your project to take a lot more effort.