Yes, multiple inheritance would be very, very nice.
So then the solution is not to have multiple smaller projects. The solution is to have one big project and trim down for different zones/areas/departments as needed.
Whatever you call it, the inherited projects, zones/depts and global, only hold what is common and should be shared. The child projects are where you put specific resources and constraints that are needed for those projects, like security settings.
IE a named query that should be available to all projects goes into global from my example, and a named query that is specific to only department2 projects goes into the department2 project, and likewise for the final projects. Shared views are in the global and zone projects, exclusive views go into the child projects where applicable. As you move down the inheritance tree, the more specific your resources should become.