When I have <button idMso="FileExit" visible="true"/> in my custom code, I receive an error stating that the control is not found.
I created a sample database...just a USysRibbons table and the options set as I have them currently. There are no other objects and no data, so all controls on the ribbon are grayed out, but you can see what the custom ribbon and File navigation pane look like with the custom ribbon xml applied. SHIFT+open is not disabled, if you need to add a data table.
Good luck!
P.S. I even tried opening as a runtime database. Although this takes care of the whole File menu thing, it also blows away my ability to export to Excel and Word...which, alas, defeats the purpose.