This is a REALLY old idea...back around 1990 WN introduced self-ticket machines. If you bought a walk-up full-Y fare, 2 drink tickets (per flight coupon, IIRC) spit out along with the ticket. If you bought the ticket through a travel agency or at the counter, no drink tickets. At the time, you could call in and make reservations without a ticket, then just buy a ticket this way at the airport on the way to your gate.

I don't recall EVER having to pay for a WN cocktail... Good idea NW!