It's as easy as 1,2,3. The ONLY catch is that you must tie a credit card or PayPal account, but you can remove it ASAP. Oh, you must also have a silver account, so gold subscribers will have to resort to making a new account or just missing out altogether.
Also, take note of the fine print, as you enable auto-renewal on your payment option. You can disable it through Xbox.com and remove it right away.
I have read elsewhere that if your PayPal or credit card is outside of the US, it won't accept your payment option. The person who said this tried through a VPN and it still rejected him, but there's always a way to bypass something, so don't be so quick to give up.
Website is quite neat actually