What do you mean with "without affecting seo"? As far as i know the url "/" itself has no special meaning for Google & CO. (Asuming you provide a sitemap and/or have incoming links somewhere. )
If you want static content (only for Robots) on "/", i'd use a javascript redirect on that page. But this page would not be ranked very heigh, because of the short (not existing) "length of stay" of visitors on that page.