I believe corrections to the above post.

Technically 500 milers can only be transfered to a traveling companion. There have been reports of exceptions or mistakes being made in this regards where it has been done. But most of the time...you have to fly with them.

Other types of complimentary upgrades can be transfered to anyone. But not 500 milers.

Also...complimentary 500 milers are only earned by Premiers and above. Anyone, regardless of status, can purchase them.