Backward AND Forward Planning

The 'due date' for all of our projects falls in the middle of the project because this specific milestone involves the customer and it is typically not a flexible date once it is set.  We have milestones and tasks before this date and milestones and tasks after this date and they need to be linked/dependent on this set 'due date' in the middle of the project.  Is there a way to set the dependencies to plan forward AND backward?