Assign widget to ZF2 layout with events

Module.php

<?php
public function onBootstrap(MvcEvent $e)
{

    /** add categories to sidebar on every request */
    $e->getApplication()->getEventManager()->attach(MvcEvent::EVENT_RENDER, function() use($e) {

        $sm = $e->getApplication()->getServiceManager();

        /** Only add it if the layout actually has a left column */
        if('layout/layout-2col-left.phtml' == $e->getViewModel()->getTemplate()) {

            /** Render it out to the sidebar in the layout */
            $sidebar = new ViewModel(array(
                'foo'=>'bar'
            ));
            $sidebar->setTemplate('layout/categories');


            $htmlOutput = $sm->get('viewrenderer')
                ->render($sidebar);

            $e->getViewModel()->sidebar .= $htmlOutput;
            $e->getViewModel()->sidebar .= 'I am on the sidebar too!';
        }
    });

}