actually i just did it!
Here's how, go on there, put in the card number, hit American Express, put your name for the Cardholder name (even though the card says "Gift card recipient") then put in the little 4 digit code, and all is done!
Problem is, you can't use 2 methods of payment, but you can buy a gift card with it, then use THAT with another method of payment.
Good luck!
PM me if you need help