Indeed, this was suggested, and
was rejected:
This feature was rejected 8/12/2012: If the sneak preview is turned on, anyone can get to your unpublished storygame by manipulating the url of another storygame. The simple way around this is to a) not include any end-game links b) turn sneak preview off (and if you have playtesters, add them as co-authors) and c) report any ratings that your unpublished storygame gets to JJJ.