Trouble with that kind of logical thinking, shorthauldad, is that it is beyond the wit/scope/authorisation of most of my client's expense controllers.

I can expense pretty much any economy ticket without a murmur. If I were to charge two tickets for the same assignment (even proving that the total was less than the semi-flex fare) then I wouldn't be reimbursed for one of those trips. So I typically don't do the thing that saves the client money, as a direct result of their rigorous-but-not-very-smart expense control policies.