Lumia Trade-in Deal

[meoge]

I traded in my 2 Lumia 920's and got 2 codes for $150 off each. I was hoping I could use them for anything in the online store, but they only show a discount when you have a Lumia 950/950XL in the cart. It may work with Lumia 650 also, but I didn't try. You also can't stack them. I've got a Lumia 640 that I'm perfectly happy with so they aren't any use to me. Any ideas on how to sell these? I'd be happy to get $100 each.