Unfortunately it does only work partly for me.

I have the following controller hierarchy:
Page -> HotelPage -> DefaultHotelPage -> CommentDefaultHotelPage

On DefaultHotelPage_Controller I implemented the index() function like this:

	public function index(){
		if($this->getField('ProvideComments') == 0){
			$ssv = new SSViewer(array('HotelPage','DefaultHotelPage_Secondary'));
			return $this->renderWith($ssv);
		}
		return array();
	}

Unfortunately this seems to prevent CommentDefaultHotelPage to render with CommentDefaultHotelPage.ss. Any ideas how this may be fixed?

I tried with different return values and even an empty index file. But as soon as I put the index file there SSViewer goes crazy.

Have you tried just

return $this->renderWith(array('HotelPage','DefaultHotelPage_Secondary'));

?