I believe you can also, if for some reason you haven't already added the gift card to your account, IMMEDIATELY after 1-click, go to your account, click on Recent orders, find the order and change the payment method and shipping method. But you have to get there fast! Once the order goes to the warehouse, which doesn't take long, it's too late. Once you call up the order, you don't have to rush. You can even cancel the order, again if you get there fast enough.
How do I know? Itchy trigger finger....
But clearly, it's much better to put the gift cards on the account as soon as you get them, LOL! Don't live on the edge like I do.
Betsy