Okay, I just did this. Too bad I can't confirm if this works until 8 weeks from now!
Anyway, I just had another realization: I have the Amex Blue but I just saw that Costco.com takes Discover. So in theory, for my next gift cards, I could get 5% back for online purchases through Discover to buy more Costco gift cards instead of just 1% using regular Amex. Anyone see flaws in this suggestion?
Sounds like it should work. 5% back at Costco is a good deal.