Delta has a close collaboration with Starbucks already. American Express has given out Starbucks gift cards occasionally in the past when denying cardmembers access due to lounge crowding. Surely they could team to buy these cards at a big discount, driving business to Starbucks and freeing up lounge space.
A Delta Sky Club Executive membership went up by $650 this year. The airline could allow members paying $1495 back into the lounge when traveling on a basic economy fare. That extra membership cost covers a lot of $8 gift cards purchased for some percentage off of that.