Request for filter for extra pages

Hello, I would like to place a request for a filter/hook to be able to add extra or external pages to the sitemap. A good place for this would be the function ‘gglstmp_prepare_sitemap’ right after the terms are added as elements.

I am wanting to integrate pages (non-post and non-term) from my guestbook plugin Gwolle Guestbook into the sitemap. I see that this plugin does not have filters for this in place. I think it would be a good option, very much in line with the extensibility of WordPress.

If you want I can provide a patch. Just let me know.