Ok, so if you did everything you have already brought up, but you also did the whole "run home to mama" web server / registration thing, wouldn't the combination work well enough that you would be say 98% covered?
Think of it this way - if the device does not have internet access to "phone home", and they hop on the install/uninstall/install merry-go-round, so what.
That's a license you never would have had, so you don't lose anything. The user would have just used the trial and uninstalled it.
However if someone gets the app in a controlled manner (ie, the Play store), and decides to give it to his mate, if his mate ALSO doesn't have internet access, then he will be ok. Until the trial runs out, then he also has to jump on the merry-go-round.
Finally, if it gets back to someone that DOES have internet access, they will be blocked because they haven't got a key. BUT if they wanted to buy one, they could.
So, what is the count?
3 installs, 1, maybe 2 license payments, and 1 or 2 people playing the install/uninstall game that you would never have got any revenue from anyway.
Sounds ok to me, but that's just my view.
Dave