Protection for "early access" builds

I have a C++ application which I want to release to a bunch of testers (<10.) I need some simple way to limit those testers from distributing it further. There's no need for super-duper hack-proof protection here, but it should be impossible for normal users to circumvent the protection. I can easily require every user to run some registration application and probably even afford to make one build per tester (though I'd rather like to avoid that.) It would be cool if I could add an time limit, but limiting circulation is definitely enough.

Some open source license managment solution would be great, but what is the easies开发者_如何转开发t way to get some protection running so people don't distribute early access builds? (Not even accidentally, i.e. someone looses his USB-stick or so)

Very, very big companies pour millions of dollars into this very thing and they cannot protect their builds enough that they don't get pirated (Windows).

Trust your testers. If you cannot trust them for this, why trust them to test your app thoroughly?

Distribute a digital certificate separately from your app, so that the app requires the digital certificate to run. This means that casually copying the app will not be a problem for you.

You don't specify your environment, but digital certificates are easy to build and distribute for just about every OS.