Simple way to get a backround. [PS]

[Demon link]

First of just place your render in the sig wherever you want it. Then CTRL+J to duplicate the render layer.Then use the single column marquee tool on the bottom render layer and place it anywhere on the render. Next press CTRL+T and drag the marquee across to the left and then to the right.

There you have it, its done, but you could make it better by distorting and brushing to improve it.