RenderView Transparency

I was wondering if it was possible to make the clipped areas of a renderview transparent. What i mean by this is: if you wanted to make a map, and it looks down on the player from really high to show the entire map, the camera will then be outside of the skybox and everything around the world brushes will be black. Is it possible to maybe make this transparent? Would mean a lot if you knew how / if it was possible.