I've thought about this one in the past. I have an old 450 lumen 800x600 DLP that got replaced by something much better.
The thought was to build a floor standing console with controls on it and the DLP housed in the back, aimed at a blank wall.
The problem:
You would need to cut a hole in your floor, pour a cement block and anchor the console to it.

Every wiggle, jiggle and bump is going to translate to 3 to 6" of movement at the projected screen. I may still try it, but I can't see it working very well until a way is found to counteract this problem.
RandyT