I think that one possible method would be to use an object as a screen, and texture it with the main camera render, so rather than rendering to the screen, you'd render a seperate camera. With that, you could put a shader through the object to ripple it, add a normal map, or bone animate it even.
The only time I did something like this was a sniper scope, or rather it was more like a magnifying glass, with tapered sides etc so it distorted what was underneath - although it was just a squished sphere (practically).
If it's a one off effect, then that's quite a stretch to do all that just so you can bend the screen - maybe there's something you can do to mask this, and use normal cameras the rest of the time. I mean, what if before any screen bending happens, the player HAS to put on some sort of gas mask, and that could be quite realistic, sound effects and everything - but it's true purpose is to provide a portal for the screen bending, so when wearing the gas mask, the camera output is textured onto a screen on the gas mask, which can bend etc. Then the player can take the mask off again when all the bending is done.
A refraction shader would probably do a great job of this.
