• Install Firefox if you don’t have it
• Open Firefox and go to Tools> Add Ons, do a search for User Agent Switcher and install it
• Restart Firefox
• Go to Google and log in to your account
• In Firefox, go to Tools and use the User Agent Switcher to select iphone 3.0 then jump to http://m.google.com/sync. You should see the Playbook listed.
• Now, go to the  Edit>Preferences>Content  menu and disable Javascript
  (If you use Windows, you will need to go to  Tools> Options>Content instead)
• Once you have disabled Javascript go back to the sync page and select your device
• You will see a screen that say something like “Send Mail As”, but with NO calendar options

Here is the bit that’s easy to miss…

Look at the address bar in your browser. There will be a long session address ending with ” multiple calendars=false “. Change the word “false” to ” true “, and then refresh the page.

The page should now have a list of calendars, select those you want to sync and hit the save button. It says you can only use one calendar but that is not the case.

You should see a message saying the device settings have changed.

Reset your browser settings again once you close that tab.