Well, I decided to call them directly and ask.. spoke to two people, the second of which had to put the phone down to discuss it with a third, and I was told it would work, but I didn't get his name and I'm not sure that was the final answer, lol.
I would love to hear from anyone who has had this work for them. Really, there's no reason it shouldn't work, as the GC should be the same as cash, but you never know, especially since we didn't pay full price for it.