Penumbra with totally 3D Graphics?

[Thaliur]

I just thought about this.
Could it be done by shader technology?
Only as an option, of course, the graphics engine could create two greyscale overlay frames from different points of view for each rendered picture, one tinted blue, one red, and put them on top of the "official" image.
I don't know how much programming work this would require, and it would most likely need lots of graphics ram and steal at least half your framerate (I guess), but if it's just a short srt of orders it would be nice to have this option.