Or do what the US DoD does. i.e. allow personnel to use their air-miles, and all other incentive programs, for personal use, with conditions:
C1200 RETAINING PROMOTIONAL ITEMS
A. General
1. A traveler on official business traveling at Government expense on the funds of an agency (see definition in Appendix A) may keep promotional material (including frequent traveler benefits such as points or miles,
upgrades, or access to carrier clubs or facilities) for personal use. This applies to promotional items received before, on, or after 31 December 2001.
2. The promotional material must be obtained under the same terms as those offered to the general public and must be at no additional Government cost.
3. Promotional items received for travel using funds other than those of an agency are not covered by this rule. Travelers should seek guidance from those funding authorities.)
Or how about something like this:
http://www.fisherhouse.org/programs/heroMiles.shtml
