Add to Google - Token

You can do this by adding any old link in your email. See instructions here:

http://stackoverflow.com/questions/10488831/link-to-add-to-google-calendar

You could design a nice button and make it clickable in an email. You would just make the link something like in the reference above:

https://www.google.com/calendar/render?action=TEMPLATE&text=Your+Event+Name&dates=20140127T224000Z/20140320T221500Z&details=For+details,+link+here:+http://www.example.com&location=Waldorf+Astoria,+301+Park+Ave+,+New+York,+NY+10022&sf=true&output=xml

It would be hard for Marketo to do this as a in-app feature because Google may change their syntax/functionality in the future without notice. We wouldn't want to break anyone if that were to happen.