[Plugin: Google XML Sitemaps] Single sitemap for subdirectory multisite?

Is there a way to combine all subdirectory sitemaps into the root site’s sitemap? I’d preferably like to automate the process, but there aren’t infinite subsites, so I’d be ok with some manual method. My main concern is that search engines interpret my site as a singular entity…

Thanks.

http://ww.wp.xz.cn/extend/plugins/google-sitemap-generator/