Sitemap for Subdomains

I realize that this plugin creates sitemaps for every subdomain which is great. Is there a way to dynamically update a sitemap that contains all my new signups? ie

blog1.weblog.com

blog2.weblog.com

and so on? I basically want Google to know each time a new subdomain is created. My current sitemap doesn’t really show much other than a couple of subpages, so how would it know to crawl all the subdomains and their sitemaps?