How's this for a frequent-flier perk: London man uses air miles for space trip. Yup, an obviously well-traveled Londoner will be aboard a Virgin Galactic suborbital flight in 2009. From the article:
Electrician Alan Watts said he flew to and from the United States on Virgin Atlantic flights more than 40 times in the past six years, earning him enough miles to take the trip into space with Virgin's space wing, London's The Sun newspaper reported Friday. The trip cost 2 million frequent flier miles, compared to the 90,000 miles required for a first-class flight from London to New York.
That's $200,000 worth of miles. Probably this wouldn't be an option for your incentive group, but wouldn't it be interesting to turn all those accumulated corporate miles into a once-in-a-lifetime experience?