VBA handle on a C# ribbon
 

When opening particular workbooks I want to add buttons to a generic
company ribbon tab, that has already been written using C# and is pre-
installed . How can I get a handle on this object? I.e. with <tab
idMso="TabHome" I can add controls to the 'Home' tab, how can this be
made to work with (something like) <tab idMso="TabMyCompany"

Many thanks.