class ContextSwitch extends \Zend_Controller_Action_Helper_AjaxContext
{
    protected $_contextKey = 'ajaxable';

    public function __construct()
    {
        parent::__construct();
        $this->addContext('ajax',array(
                    'suffix'    => 'ajax',
                    'headers'   => array('Content-Type' => 'application/jsonp'),
                    'callbacks' => array(
                        'init' => array($this,"initAjax"),
                    )
                  	));
    }
    public function initAjax(){
    	\Zend_Controller_Action_HelperBroker::getStaticHelper('layout')->setLayout('ajax');
  	}
}