By using CalDav, as explained here http://wiki.meego.com/Migrating_from...ogle_Calendars

I synced my primary (my own) calendar with MfE, but all additional calendars with
https://www.google.com/calendar/dav/username/

(Using the other person's Google username worked for me, didn't even have to do the uuid@group.calendar.google.com bit that the wiki page mentions).