Do you have a plugin that's similar to Sidebar Pro but for themes?

My new site will be a hybrid, where I will blog about both my professional and personal interests (as they greatly overlap). Ideally, because my site will be an eclectic mix of subject matter, I would like to have a different theme for each major category. Do you know if this is possible, with any of your plugins, or can you recommend any? I don't really want to activate multi-site on this domain!