Role inheritance from master (parent) Project Area to child Project Area

I am using RTC 4.0.1 and I have a master (parent) project area which has its process configuration inherited by a large number of child project areas.

The master project area has a number of different roles defined eg..

workflow_browse

workflow_edit

workflow_edit_2

administrators_1

administrators_2

The problem I have is that I do not want all roles to be inherited by the child project areas, I would like the 'administrator' roles to only be visible within the master project area. So when users of child project areas are adding roles to their members they do not see the administrator roles in their list of "roles to add".

This sounds like it should be simple to do but I couldn't find a way so any advice would be great!

Thanks..