Hey, and welcome to FT!

If he needs a visa and it's hard to obtain one on such short notice, you can buy a refundable ticket to anywhere for a flight that departs from the same terminal as his flight to the U.S. on that day. He can transfer to that terminal via the airside bus if necessary. Meet there, hang out, drink coffee, whatever. Use an airline lounge if one of you has access to it. (If you "buy' a business or first class ticket, you will.) Then walk out of the secure area, phone the airline or go to one of their landside service desks, and get your money back.

If anyone asks you why (which they won't, refundable means just that) you can say that you were sitting in the terminal with a friend and lost track of the time, you got a call that your meeting in Chicago was cancelled, or your gerbil died and you can't bear the sorrow must stay in London to console his widow.