Don't know if this has been tried before, but here's an idea... instead of using _url to disable a game from playing, (ie asking for your game to be decompiled before it is uploaded to the www) why not make your _url check simply report offending websites with a getURL to a php script running on your site that takes the value of the flash _url as a parameter.

ie, getURL("" + _url , "_blank", "POST");

Your php script could then notify you via email with the domain name when a new domain starts running your game (plus the IP of the person who first tested it) or whatever you like.

Just an idea.