Once iOS 9 launches next week, Discover will be offering 10% cashback on all in-store purchase when using Apple Pay, up to $10,000.
I'm assuming most retailers that sell $500 Visa/MC gift cards accept Apple Pay.
http://www.businesswire.com/news/hom...0909006702/en/
From September 16, to the end of the year, cardmembers who pay with their Discover card using Apple Pay will automatically earn an extra 10% Cashback Bonus on up to $10,000 of in-store purchases. Discover it Miles, Miles and Escape cardmembers will earn an extra 10 miles per dollar on up to $10,000 of in-store purchases.