It is possible to accomplish your goal, but unfortunately probably not in any way that will help you.
For example, consider the following policies:
- Email Provider: Each person must only register for a single email address.
- Country Government: Each person must only obtain one passport.
Typically the Email policy is easy to circumvent, and the Passport policy is difficult to circumvent. The reason is due to the difference in the types of verification. To obtain an email address you typically don't need much verification at all, whereas you do when applying for a passport. If the Email Provider required you to show your passport in person in order to get an email address, then it too would become difficult to circumvent.
So, how far are you willing to go to verify that each node has only generated a single identity? It can be done, but it might very well exceed your usefulness threshold.
You're probably going to need a unique marker that differs in every mobile device and cannot be spoofed. I'm not sure if this exists...