Maybe the unlock system is just too generous to allow users to activate LFS all the time?
Maybe it needs to be more ruthless and attach IDs to each unlock and automatically deactivate old unlocks from the Master Server at a certain limit (ie 3 unlocks and a new unlock invalidates the oldest from the master server). And then rather than give a new one each week, give a new one every month.
Adds support costs when people have issues and needs to ask for new unlocks, but presents a barrier in people sharing accounts.