I have a dilemma. I want to add nofollow to all the sidebar links, but only if I view single post or single page, not homepage. On the homepage every link on the sidebar should be followed because those links act as a category. I want to enable nofollow on single posts and pages to prevent PR flow. These pages should pass PR only to the links in the article itself. How can this be accomplished? Possibly without editing the core files of wordpress.