I was astonished -- really astonished -- to discover that all I had to do to revive 3K forfeited miles was open a Barclays US Air MasterCard account. I had actually just done this anyway to snag an extra 50K soon-to-be AA miles before the program merger. The forfeited miles reposted a couple of days ago.
This was all a fringe benefit of linking my US and AA accounts since I wouldn't have looked at my US account otherwise and I had thought the miles were gone for ever. Luckily for me, the US website is actually very, very clear on this topic.