~via BB (wap.pinstack.com)~ IKnow the newer 88xx and 83xx have a new Manage Networks option that I think would solve your problem. They now have the ability to shut off just data service instead of all transmitions.
I've never tried it, but that's my understanding.
If they are on older devices I can only suggest creating a profile that doesn't notify them of new messages. And I believe one of the email options is to NOT have the number of unread messages post on the home screen.
I hope your answer is somewhere here.