Master Routes over multiple business units for same item.

  We have a business unit that's trying to create their own routing on an item that has a Master Route assigned to another business unit.  Is there a way to have the business unit that's setting up routing on the item without the master route from the other business unit being tied to it?  I know for that business unit that is trying to add their own routing we can turn off Master Routes and they can then add, however, I'm sure they will still want to proceed with using master routes.

Thank you.