This will assign all of your users an activation password. None of your users will know this has been done. You can then contact the 80 users to inform them of the password/activation process.
Didn't think about that. Not a bad solution. For the 1920 users that don't get a new device, the activation password will just expire after 48 hours, they won't notice anything.
The only downside of this is that one of the 80 users could activate with his bosses e-mail address (as the activation password is the same for everybody) and then read his bosses emails. But this is probably rather unlikely.