The problem is you shouldn't even care about NDAs regarding outsourcing your prototype. It's about as bad as requiring an NDA to disclose your idea to potential cofounders. In the mass majority of cases, no one cares and if you outsource overseas, I don't see a high correlation with people jacking your idea to outrun you in building your startup. I think you're going about it the wrong way. The likelihood of someone pulling a "social network zuck" on you, is very unlikely, especially for outsourcing a prototype.

As for possibly getting a prototype done, I don't understand the comment here. If you outsource the work, you pay X and they code Y and you guys do the exchange. There's no inheriting or whatever you're referring to. Sounds more like you're trying to recruit employees or something than to purely just get the prototype finished.