OSGI and Vaadin, Modular theme problem

Hi. I’m using Vaadin and Osgi (Apache felix) to provide a modular system.
I’m following there two guide:

  1. Create a Modular Vaadin Application with OSGi

  2. Chris Brind’s Article

Basically it works, I use servlet to register Vaadin Application and use Fragment-Bundle to provide customer themes.
The question is:
In a mudular system, each module should contain some customer themes and resource.
I can attach them to /VAADIN path by using Fragment-Bundle.
But the theme can only be set in the base Application with setTheme method.
And other module (plugin, addon) provied their content as Component can’t use setTheme, and I can’t find a way to merge their css into base Application’s css file.

I think I may miss something, please help.