Exclude nodes with no alias?

I have a site where I use reptags and some internal nodes to provide common content on multiple pages. Those common content nodes have no alias, and don't really make sense to a user by themselves - can I make xmlsitemap NOT expose these nodes? (so it only shows nodes that have a URL alias?) They aren't otherwise referred to anywhere else in the site, so this is the only way they'd show up for the outside world...