Try this placed inside the event_view page template (customise it in the ZMI) after the vCal and iCal links:
<a href="#"
tal:attributes="href python:'http://www.google.com/calendar/event?action=TEMPLATE'
+'&text='+here.title
+'&dates='+here.start().toZone('UTC').ISO8601().replace('-','').replace(':','').split('+')[0]+'Z/'
+here.end().toZone('UTC').ISO8601().replace('-','').replace(':','').split('+')[0]+'Z'
+'&location='+here.location
+'&details='+here.getRawDescription()+'<br />'+here.getRawText()
+'&trp=true'
+'&sprop=website:'+here.event_url()
+'&sprop=name:'+here.contact_name();"
title="Add this event to Google Calendar"
target="_blank"
style="background-image: none; padding: 0px;"
>
<img src="https://www.google.com/calendar/images/ext/gc_button1.gif" alt="Add to Google Calendar" width="50" height="13" />
</a>
Arjun Dixit
showbox.onl mobdro.one dltutuapp.com