Hi Ian,
Can you please clarify where you trying to display that list of Customers: when you develop the query to use it as a restriction or when user runs the query.
If it's when user runs the Query then it again depends on what front-end you are using. Usually you can disable Hierarchy view. You can also put navigational attribute GROUP as a free characteristics and user will be able to restrict it there.
Regards,
Gersh
