Set featured image as background

First things first, thank you for a wonderful theme – it’s not only very good looking, but also pretty co-operative to modify, which is not a common case.

There is one thing I can’t achieve though. I’m trying to change the background image to a featured post image so it would change for every post and display the default bg.jpg for homepage, archives etc. Played with “bg-image master” div on header.php with ideas from here and here, but with no luck…

Thank you!