I'm running a setup with 3 monitors (in windowed mode, don't know if it supports anything like eyefinity/surround but I don't have a rig anyway) and the letterboxing (black bars) that normally shows up during in-engine cutscenes actually doesn't extend all the way to the sides due to the resolution of the game window greatly exceeding the actual size of the bars. They look like a 2D element, probably on the HUD layer.

If anyone with a bit of know-how could at least point me in the right direction, I might be able to do some tinkering on my own.