under these circumstances where they absolutely won't reimburse F/J without two or three or four levels of management/leadership approval (and usually those have to be in advance), it's not difficult to find a Y fare that's rather more than the default but still within policy

I don't recall the exact itinerary, but a couple months ago the Concur search returned the lowest Y fare (~$187) on NK with a 5-hour layover in LAS and a midnight arrival ... a reasonably-timed connection on DL was ~$310 (with F ~$460), and "Lowest Logical Fare" was DL nonstop at ~$385