Content should fill area when blocks are disabled.

When I disable all sidebar blocks, I would like the content area to fill this part of layout (in this case, I'm using a timeline view, and want the horizontal display of the timeline to fill the content area when no sidebar is needed). Can this be solved in the CSS or the page.tpl.php? I tried deleting the sidebar and setting main and content to 100% width, but this hack didn't quite do the trick. I thought there might be a clean way the Elements theme developers could implement this.