If you know which of the three or four tickets are scarce (something that could easily be determined by a few enthusiasts online by collating their ticket data

If you know which of the three or four tickets are scarce (something that could easily be determined by a few enthusiasts online by collating their ticket data), winning a grand prize is as simple as buying more McDonalds until you have the tickets to complete the set. The trick is that most people who receive the rare tickets won't know and will either bin them or not obtain the remaining tickets.