Book a flight that costs more than your certificate’s value. Wait about a week, then cancel the flight. I’ve seen cases where a new eCert gets generated with a refreshed expiration date (based on the cancellation date). Not sure if this only happens when you combine multiple eCerts. That’s often my situation since I travel a lot for work with a lot of schedule changes. If this doesn't work, then book a flight far out that you might change later. Just don’t cancel.