Once had a woman come in with an unscannable TM discount card. She told me they just type it in at her store. I said I was sorry, but we weren't allowed to do that at our store. She wanted to talk to the GSTL, who backed me up. My GSTL basically told her, there is no reason to go weeks and weeks with a discount card that won't scan, just go onto eHR and order a new one. You should have it by the next payday.
And to OP, the guy using your discount is really not your friend, find a new friend who won't take advantage of you.