A única maneira de fazer isso foi usando Spanning Sync .
Spanning Sync 3 is the one app that syncs both iCal with Google Calendar and Address Book with Google Contacts
Update: as of 7/24/2012, Spanning Sync has announced the end of life of their product. More details here: http://blog.spanningsync.com/2012/07/end-of-the-line-for-spanning-sync.html