Sorry, I don't have an answer for you, but maybe if I try to clarify your question a little, someone will provide a good solution, which I'd like to see myself.
Tell me if I'm wrong about your question....
When you buy a software product, there is a product key code that usually comes with the original packaging, and that you must enter during installation in order to activate the software on the user's machine. ie: copywrite protection.
I've never packaged a product for distribution like this, but it seems like the packaging process would include this functionality, or maybe there's a third party product that manages it - if not, it seems like this would be an area of opportunity for an enterprizing programmer...