Ability to create ad hoc aggregations via multi-selections in filters

I want the ability to narrow down the summaries I see for a parent. I need to give end users the option to see summaries for any combinations of list elements in any dashboards and modules. At the same time, users should be able to select several list items for tables to synchronize with all of them simultaneously.

If you select a parent, you see all summaries for the child, but I want to be able to have the ability to select multiple parents, or multiple children, while having the ability to exclude others.

For example here’s a simple hierarchy:

• Region 1
  • Client 1
  • Client 2
  • Client 3
• Region 2
  • Client 4
  • Client 5
  • Client 6
• Region 3
  • Client 7
  • Client 8
  • Client 9

List is in page selector: When I select a region, I can see summary for all clients inside this region. We want to have an option to select for example “Client 1+Client 2” or “Region 1+Region 2” and be able to see the summaries only for the selected list elements.
List is in rows/columns: When I select a Region and there is a module with synchronized Clients dimension in the dashboard, I will see the data for each client inside the selected region. We want to have an option to select for example “Region 1+Region 2” and see the synchronized dimension for all the clients inside selected Region elements.
Graphs: The first two points should also apply for any graph.