The only foolproof method for making sure frequent flyer miles don't go to waste is to-brace yourself!-use them. Go ahead and book them for a future date; the dates don't matter.
Though there are a lot of easy ways to keep miles active, from spending or buying miles with more forgiving programs, that's not true for every airline. For instance, Asiana miles definitively expire after 10 years, and 12 years for those that have status on the airline.
(Singapore Airlines has a very similar policy; their frequent flyer program has miles expire after three years. They do allow a one-time extension for a fee.)
Case in point: I have 21,415 miles expiring by the end of the year. That gives me three months to figure something out, and my travel is already planned, booked and accounted for. (It seems like my entire life is already planned, booked and accounted for, though that's another story!)
The only option left is to book a flight as far out as possible in 2025, and then change those flights when I figure out next year's plans.
It would be safer to book a trip I'm more likely to take, too, just in case things go awry.
So yes, you can wheel and deal all you want, but using them, or even gifting them, would be a far better use than letting them go to waste.
