You need to tell Zend_View where your helpers are, following your example (assuming your library is on drive w:\, for the sake of the example):
Code:
// instantiate the view and save Zend_View object to a variable
$view = new Zend_View();
// add to the helper path
$view->addHelperPath('W:\library\Addon\View\Helper', 'Addon_View_Helper');
$renderer = Zend_Controller_Action_HelperBroker::getStaticHelper('viewRenderer');
$renderer->setView($view);