How to add my own toolbar ?

OK, so I modified the toolbar (by hacking the toolbar2 class in the TK backend).
But I can just make that a new class and call it MyToolbar.
How can I now conveniently have matplotlib use this toolbar?
In the rc file you can define 'classic' or 'toolbar2', but not
'customtoolbar' or something like that.
I looked at the 'embedded_in_tk' example. That would work, but then I
lose a lot of other functionality. Is it possible to just set a flag
and have matplotlib read my toolbar (asking too much maybe?).