Here is how I modified the function responseFilterContent in /usr/share/nginx/atom/apps/qubit/config/qubitConfiguration.class.php
public function responseFilterContent(sfEvent $event, $content)
{
ProjectConfiguration::getActive()->loadHelpers('Javascript');
$new_content = str_ireplace('</head>', "
<!-- ENACIT SB Matomo -->
<script type='text/javascript'>
var _paq = window._paq || [];
/* tracker methods like 'setCustomDimension' should be called before 'trackPageView' */
_paq.push(['trackPageView']);
_paq.push(['enableLinkTracking']);
(function() {
var u='
https://our-matomo-server.example.com/piwik/';
_paq.push(['setTrackerUrl', u+'matomo.php']);
_paq.push(['setSiteId', '123']);
var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0];
g.type='text/javascript'; g.async=true; g.defer=true; g.src=u+'matomo.js'; s.parentNode.insertBefore(g,s);
})();
</script>
<noscript><p><img src='
https://our-matomo-server.example.com/piwik/matomo.php?idsite=123&rec=1' style='border:0;' alt='' /></p></noscript>
<!-- End Matomo Code -->
</head>", $content);
return str_ireplace('</head>', javascript_tag('jQuery.extend(Qubit, '.json_encode(array('relativeUrlRoot' => sfContext::getInstance()->request->getRelativeUrlRoot())).');').'</head>', $new_content);
}