'Fraid so. Take a look at Volume 67, Decisions of the Comptroller General of the United States, page 79 - 83 [67 Comp. Gen. 79 (1987)]. That decision (B-220542) holds five named Agency for International Development employees personally liable to the government for the value of tickets they got by redeeming frequent flyer miles earned from official government travel. That decision also surveys prior decisions by the Comptroller General dating back to 1984, including holdings that employees cannot use such miles for personal travel even if the government was unable to take advantage of the miles before they expired.