As a developer putting on the user spectacles, I find your approach not convincing. If I click on a settings button, I expect a well-designed dialog, not to be thrown into backstage view. On the other hand - as a developr I'm much more at ease with a well-designed Windows Form than with the controls Microsoft provides for the backstage user interface; I guess you'll find there more limitations then you like.
As far as I understand your question, you want to have two different entry points to your settings dialogue - one from a button in the ribbon, and another from a point in the backstage view. Why not combining and showing from both positions the same form? Also Microsoft provides you with additional dialogues, if you click on controls in the backstage view.
Technically:
If you want to start the action of a ribbon control, you can use the "ExecuteMSO" command of the application.commmandbar object, e.g. in Word you may use
Application.CommandBars.ExecuteMso "ApplicationOptionsDialog"
to open this dialogue. However, I've done a limited test to call a custom button in backstage view, and it failed. Sol I guess that you can use ExecuteMSO only for built-in commands.