Customize Ribbon with excel interop

Hi everyone,

I am developing a c# application, which is created from an excel workbook.
In the VBA code of the workbook, my assembly (a class library project) is
created, a class instance is created and a method is called. To this method
an Application object is passed. So I can register on excel events and
interact with excel. I can change or add menus, do things when workbooks are
opened, etc.

Now my application should also work with excel 2007. But in excel 2007 there
is no "standard" menu, but there is the ribbon. So I need to change the
ribbon from my c# project. I have a reference to the excel application.

Note: I tried to do that with an 2007 addin, and returned the XML file which
worked perfect. But I can't use the add in approach, because my application
is not the creator of the excel application. So I need to change the ribbon
by interacting with the application object (or objects reling in the
application object).

So can anyone tell me, if this is possible, and if yes, how I can realize
that?

Thanks for help,
Regards