BTW, I found this thread because I was running into the same 'data storage full' error, and I just did the following to get this to work...

Went to the iphoneselect page to select one of the sub-calendars I was interested in (work-related calendar).

https://www.google.com/calendar/iphoneselect

Added the related CalDAV account on the N9...

User: myusername@some.domain (google apps corporate account)
Password: <my password>
URL: https://www.google.com/calendar/dav/

The N9 did the usual check before it added the account, and then I saw both calendars being added (the main myusername@some.domain calendar, as well as the sub-calendar I toggled on with the iphoneselect tool)

Edit: I even went back into my 'personal' google caldav sync, and just changed the URL to https://www.google.com/calendar/dav/ just because that URL seems very clean and intuitive.

HTH.