Sorry, but the BES only syncs the Inbox on the activation that I am aware of. I've never seen it sync anything else. Remember that the BES will only sync so much mail as part of the Enterprise Activation, the default is 200 messages or 5 days worth, whatever comes first. If you enable other folders how will the BES know what messages to sync from what folders? The logic won't allow it to happen.
That's how the BES is designed.