dyablohunter on "2 or 3 column grid layout for Twenty Twelve"

I came across this post:
http://www.transformationpowertools.com/wordpress/posts-in-two-columns-twenty-twelve#comment-24185

And it does work for the latest version of Twenty Twelve, with the exception that I couldn't figure out how to make the articles go under each other and not align at the end of the longest article, while keeping the responsiveness of the theme.

The author of the article suggested I use another post of his:
http://www.transformationpowertools.com/wordpress/playing-with-columns-stacking-posts-grid-style

But this one needs to be adapted to the Twenty Twelve, and I really am not that good with PHP.

Can someone please give me a solution to this? I would really appreciate it.

Thank you.