For anyone with an American Express credit card, they have an offer for "Get a one-time $5 statement credit by using your enrolled Card to make a single purchase of $5 or more on Google Play by 8/31/2015."

Also an offer for "Get a one-time $5 statement credit by using your enrolled Card to spend a total of $5 or more on iTunes by 8/31/2015."

You'd need to login to your account and add the offers from the "Amex Offers & Benefits" box first to get the credit.