The App Developer Group is preparing a None Disclosure Agreement (NDA) which can be used amongst ourselves for situations like this. If you would like to help organise this we already have around 50 members that might be interested in helping.
This is currently only in discussion at the moment but I thought I would mention it to you as you might want to actively advertise this idea to our group and perhaps we can help achieve this together?
If you're interested then maybe mention it on our thread here:
http://forum.thegamecreators.com/?m=forum_view&t=187597&b=41
Or you could email me to discuss the idea further?