Just to go back on topic and not he ethics of the ordering system. Zen Cart have an option where people “can pick up instore”.

Replace the words in the English file from

“Buy Now” to “Order now”

Change to a couple images giving the impression or ordering not buying.

And option to pay instore.

Can’t see any great difficulty in customising it to the way you want it. I would’ent look for id cards just the order confirmation would do