Add an Item to "Post Popup Menu"

[memobug]

I've searched the templates and looked in the JavaScript includes, but I can't seemt to find out how to add an item to the post popup menu. This is the menu that appears when you click on a username next to a post. It has stuff like

1. View Public Profile
2. Send a Private Message to <user>
3. Find more posts by <user>
4. Add <user> to Buddy List
5. Stuff I want to Add here

The html dump starts like this:
<!-- post popup menu -->
<div class="vbmenu_popup" id="postmenu__menu" style="display:none">

But I can't find the menu!

Regards,

Matt