One word: Vuze can do it! It’s not what Vuze’s main purpose is, but it works.
I decided to renew my Xbox Live account. My credit card had expired. Pick the gamer card, account management, membership, payment options… And I ended in a sort of loop: I could redeem codes which I did not have, add a card (which I tried to do but at the very end the system refused it because “it already existed”) and look at my existing credit card. Only after having wasted enough time did I realize that on the screen where it shows you the card you can pick payment options if you want to edit the card, and that’s on the blue button. Everything else is on the green (select) or red button (back).