This is a fixed two column theme. In the code you can only have one sidebar – either left or right. If you want to have two sidebars, that would make it a three column theme, and you’d have to modify the code to do so.
I don’t know how to do that, but if you haven’t done so, email the author – he might be able to help, but he is pretty hands off and the theme is mostly “as is”.
If you do find an answer, I’d love to know.
bertandpatty.com
Good luck
Paul