Adding padding before sidebar border?

I have a layout where the sidebars appear only on some pages. On pages where there are no sidebars, I'd like the center column to have no padding on the right side. I was hoping to avoid having to use a css insert to specify a revised padding listing each of those pages. I hoped I could deal with it via the sidebar styling in ATO or a css insert (because without it in the center column, text runs up to the border, of course). This site is getting handed off to a client, so I'd like to have it automatically be right if he adds a page of one type or the other.

Is it possible to add some margin or padding before the border in the right sidebar? I know I can push the text right relative to the border with the padding setting in ATO sidebar settings, but can I get space on both the left and right of that border in ATO or a css insert.

The page I'm working on is this, but it might change as I'm trying things: http://amirparsa.net/literary-oeuvre