[Livven]

There's a very strong hint on the site. If you're a developer you should be able to figure it out easily, if you're not a developer you probably won't know how to "remove the disabled attribute" anyway ;)

[Tomdarkness]

All it takes is someone to post a few step by step instructions and anyone could re-enable the button regardless of their skills. Hopefully people won't ruin this offer and do that though.

[Bradosaur]

I'm pleased to see that slickdeals and fatwallet both have threads about this deal, but no one has spoiled the puzzle yet.

[IgorPartola]

Or a Chrome plugin :)

[Aloisius]

It is easy enough to write a small bookmarklet that anyone can paste into the window to flip off the disabled field. Once that gets into the wild, I can't imagine this offer will last.

[Bradosaur]

Fortunately, it sold out before that became a problem.