Sorry, that’s not possible with this plugin. It is designed to create a sitemap index on sitemap.xml which will in turn reference other sitemaps, including different types of urls on your site. Posts, pages, category and tag archives…

Why do you actually need to have every URL in one sitemap? If you submit the main index sitemap.xml to Google and Bing, they will follow the referenced sitemaps and report about each one in your Webmaster Tools account automatically.