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Try this: Place your render in, and duplicate it a few times. Hide all of them but 1. Smudge a little, and set on lighten or something. Un-hide the next one, do the same thing, try different settings. Move them around, go to filter-> distort, pick one. And on the last one, leave it on normal blending and see how it turns out.
If you still have the psd, try placing the render BEHIND one of those splatters or something. It's always good to start out with the render, and add the background so you can kind of add colors and C4Ds according to the render.
You can try placing a Gradient Map, it should blend it a bit. If you would like to remove parts of the gradient map, take a black brush and paint over the spots you'd like to remove (change opacity of the brush according to how much you would like to remove).
I hope I helped, you can PM me or add my msn.