Actually, you *can* do this- you just can't eject it, and the pictures come out backwards. A little creative shuffling around inside a film change bag can produce some rather remarkable results:

https://picasaweb.google.com/closeen...DO0bCL9cvtgwE#

There's a frame of Impossible PX680 in there for comparison; all shot on the same day, in the same camera (though the Instax shots were transferred back into the Instax 200 for processing).