Yeah, use a screen overlay (I think it's called). I know that alexroyce did something similar to make cs_noir appear to be in black and white.
Also cs_noir came out before color correction was apart of the engine.
Initially I was going to make a snarky comment about not being able to tell portals apart, but the result is, from color decomposition, a white and a black portal.
I think it's possible to recolor the world using the Select HSV tool via the colorcorrectionui.
You would do the same sort of thing, find the shader that the blur effect is used and make a fish-eye like material to be overlayed on the screen.