Blogs Directory - Filter to Hide Sites

I have a multisite that allows visitors to create their own websites (Pro Sites). I have many people signing up, however, most are just kicking the tires. Since these people rarely change their site description, I would like to hide all blogs that have the default site description. Ideally, I would like to add a filter to functions.php that will accomplish this. If not, directly editing the plugin files is fine too.