You can only sync with your default calendar. You can't change the default calendar in google to another calendar. So the fact you can only synch with one calendar and it's the default, you are stuck. You're in the same boat as the rest of us. If you do decide to synch with your default calendar, you'll notice many other bugs (e.g. something as simple as calendar notes - kinda important ya think - don't synch from server to N900, reminders don't set right nor do they update,, among many other things). Pretty much unusable as a calendar other than just seeing what might have been at one point and hope it still is.

You can try nuevasync, but I don't recommend it. Did a lot of testing and MfE is the lesser of two evils (and that's not saying much). Nuevasync has issues with the N900 that they finally admitted to in the forum - I had a TON of problems with contacts and calendars so abated the entire idea. Some seem to have luck - and you can synch multiple calendars. Perhaps their contacts/calendars aren't as busy/heavily used/edited as much as mine. I dunno, but if you want to experiment, calendar/contacts are free and I think you get up to 10 calendars - shared will show up as a choice.

Good luck.