Originally Posted by
GrumpyYoungMan
Buy a ticket with miles and cancel/re-deposit?
This.
Book a simple award ticket for some date way off in the future, wait till it fully tickets and the miles are deducted, then cancel it for a full refund of the miles/taxes. Expiration date is now reset.
Alternatively there is of course a long running thread with many answers to this same question...
Prevent AA miles / account from expiring / expiration & spend for other than flying