I sorta did that, I copied my render 3 times, one on the right, middle, and left, and smudged it. I also jittered the render as well 3 times, and one thing I do a lot (which may not be a good thing) is to get a pretty high-size paintbrush and just do a big, random line, then run radial blur deluxe on the max amount and the minimum steps, that makes a nice texture that you can lower the opacity a bit and have a nice, subtle addition to your background