The documentation around Office 2007 ribbon customization is still a bit sparse. I’ve been trying to add a new entry under the Save As menu in the Office Menu, and after a fair amount of trial and error, I found a way to do that.
Here is the XML:
The odd part, in my inexperienced view, is referencing the same “FileSaveAsMenu” id in both the splitButton and the menu elements.
I searched in vain for an XML file that contains the definition of the complete default ribbon. Having that would have made this and other customizations much easier. A similar strategy ought to work for other pop-up style items, like Print, Prepare, Send, etc.