I have a wordpress blog as part of a larger site, and adding the individual pages from that site to the sitemap generated by this plugin is a total PITA. So I have two suggestions, either of which will solve the issue:
1. Make the plugin capable of merging its generated sitemap with another sitemap from a specified file.
2. Allow the sitemap generator to scan for other pages to add, merging the blog and non-blog results.
The first is preferable.