Specifying a camera using ScreenShotMovie and changing capture rate while not affecting playback rate

I have two cameras in my scene, one overhead and the main camera attached to the Player. Using the script located at http://www.unifycommunity.com/wiki/index.php?title=ScreenShotMovie, I want to be able to capture screenshots with the overhead camera (running in the background), while the Player is moving around.

What happens at the moment is that the script captures images from whatever camera is 'active' in the viewport.

I also want to be able to capture only 5 frames (for example) per second, while not affecting the playback rate, 24 fps (for example).

Thanks in advance.