I am learning ZF2.0 beta. In ZF1 we can change layout on the fly in controller:
Zend_Layout::getMvcInstance()->setLayout('layoutname');
But in ZF2.0 Zend\Layout class doesn't has method getMvcInstance(). I think that it can be made using dependency injections but not sure.
The ZF2 is heavily under development and no guarantee can be made the way it works now, will be the way it works when ZF2 reaches a stable state.
However, the new view layer from Zend\Mvc is recently merged so you should be able to do this now (with current master):
public function somethingAction ()
{
// Do some intelligent work
$this->layout('layout/different');
}