Render Modal form with widget field that requires renderJS

ModalandrenderJS

 <?php
 protected function executeModalFormAjax(sfWebRequest $request)
  {
  	eval(sprintf
  	(
  		'$form = new %sForm();',
  		$request->getParameter('form')
  	));
  	return (string) $form.' <script>'.$form['user_id']->renderJS().'</script>';
  }