Consider this: A week during a vacation, when plenty of kids will be home from school, and that has been publicized for months, where a key is officially released publicly, a key that does *not* work for offline mode, and after a week is banned. And it's name is unchangably set to Guest_######.
In my opinion, such a stunt would be *far* more likely to make money than raising/lowering the price, or forcing existing users to pay again (but possibly less money than auctioning a few IDs less than 100 might make), or restricting the ability to use add-ons in the demo.
The best part is that it would be both temporary and repeatable, so if it fails it ends shortly after, and if it succeeds, it can be done again at a later date. Either way, it might cause temporarily increased publicity.
It *would* require a better server list, however, for example splitting the creator's name into it's own column and possibly adding a search option.