I realize you say that you don't care about the patents issue, but that's really the only issue. Even if you were to aquire a 3rd party ribbon control, Microsoft has the patents on it and can come after you for violating them. They've explicitly come out and said that people can use it for non-competing products.
The Office UI license restrictions are for the concept of the ribbon, not just MFC's specific implementation of it. See this page for more information.
