As I already have code to add button specifications to a display element it was pretty simple to add ButtonSpec definitions to the tab bar.
You will almost certainly want to use this ability to add your own additional buttons to the ribbon. Office 2007 applications already do this by having a help button on the right hand side of the tabs area.
Here is a ribbon where I have defined a button spec for the right hand side that has an image and some text. There is also a button spec defined for the left hand side that is just an image.
When using with an MDI application the pendant buttons appear on the right hand side of any buttons that you define. In the same way as Excel 2007 works.
Finally to prove the left hand button is really working, here it is highlighted.