Flickr member bricolage.108 hacked a 35mm trashcam into a double-sided lens/pinhole monster. He writes:
If using a normal film roll this camera takes redscaled ["redscale" is where you shoot the film backwards, so the light gets filtered through the antihalation layers before hitting the emulsion and turns the image red/orange or yellow, depending on the film] pinholes from one side, and trashy lens shots on the other. It also makes doubles, exposing both sides of the film.
The same way if i redscale the roll first, i can take redcale shots using the lens and "normal" pinholes, on the same roll with the same camera.
I can, for example overlap the same subject using two "different cameras" and techniques or (and this i think it’s conceptually interesting) create (simultaneously) an image where the shot and what’s "behind the camera" are both visible.
Here’s an image he made with it, more here.