Pay through the Humble Bundle Widget
Below Widget offers you the same game account purchase but without the requirement to register a website account. You may still reedem the included forum title at a later point through the game account manager.
Please note: Once purchased, you'll be able to redeem a key, which is a specially prepared hyperlink. Simply copy the whole text into your browsers address bar. It will lead you to the game account manager where you can set up your game account and download the game.