Not directly related to Weathermap, but a lot of WM users are Cacti users... I just released the first version of SuperLinks, which is a plugin to allow you to add arbitrary content into Cacti as additional tabs, or menu items. It can save you the trouble of writing your own plugin, since you can also include PHP content into a new tab. You can also limit access per-page to individual users or groups of users, and it even produces the tab images for you.