Is there some way to sync only Reminders to iCloud? Under Mountain Lion, syncing Reminders to iCloud is linked to syncing Calendars for some reason:

In contrast, under iOS (version 5), you're able to sync Reminders to iCloud separately:

I sync my Calendars to a Google Calendar, and my Reminders to iCloud on my iOS devices.  However, in Mountain Lion, this doesn't seem to be possible.
Is there some workaround to the limitation in the preference pane in OS X?
Yes you can. Just add your google account from System Preferences as usual. Then open iCal > Preferences > Accounts > iCloud and untick "Enable this account"