How would you demonstrate that your ticket redemption value is $480? If you need to book a ticket, then print out your receipt and then cancel the ticket to get "proof" that it was $480, then I think you're definitely beyond the borderline of grey area. Essentially, if you have to "create" a receipt, it seems questionable.
If there is no need to make up a receipt, and can easily claim the cost of the ticket, then I think it should not be an issue.
I'd favor pocketing $480 and parting ways w/ 25K miles, but at the same time, I wouldn't do it if it required "gaming" the expense claim.