Top left shows the view with the camera in the final position.
Top right shows a view from the side to reveal the construction.
Bottom shows the three pieces of aluminum that were used.

Final image was turned upside down so that the fake corner is at the bottom where it is less obvious, the background darkened to black, a little bit of cloning to fix blown out highlights and rough edges. Light is from a flash at the left with mirror on the right side.