According to this FlyerTalk thread, British Airways is offering 5,000 bonus miles for adding an authorized user to the Chase British Airways Visa card by May 15. An additional authorized user can be added by calling 800-577-0633. Apparently this bonus can be earned a maximum of one time per card and it takes 6-8 weeks for the bonus miles to post. Since no social security number is required you can add just about anyone (or anything).
No guarantee it will work, but then again there’s nothing to lose. This has the potential to add 15,000 miles to my British Airways household account.