Buy a song on iTunes through the AAdvantage shopping portal. A $1 song will earn you 3 miles, enough to extend mileage expiration. You can also get mileage for e-gift card purchases.
To do so, ensure that you access iTunes through the AAdvantage eshopping mall.
They can take 6 weeks to post, so I'd make the purchase quickly to ensure that the miles come through before your miles expire to make things easier.
Or see
this post in the AA forum FAQ, which links to this thread:
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