According this Blog from Microsoft, it looks like many of the customization features are being made available with the 2010 release of MS Office. There appears to be very little published code or methods for automating what shows up in the navigation pane.
http://blogs.technet.com/office2010/archive/2009/11/09/making-the-ribbon-mine.aspxHaving said that, there are some developers who have published their customization routines for MS Access 2007. The developer at this link is sharing some of what has done with MS Outlook using C++ and VB.Net.
http://www.add-in-express.com/creating-addins-blog/2009/04/10/outlook-navigation-pane-customizing/This link has the most free published code on the ribbon interface. You can try doing a search on the navigation pane and see what is available.
http://www.accessribbon.de/en/index.php?Welcome