Hierarchy and Permissions

Hierarchy and Permissions

I need to be able to set privacy permissions on a user by user basis. What I am trying to do is: I want to be able to share leads that are assigned to John Doe with Jane Smith but not Jane Doe and I don't want Jane Smith to see Jane Doe's leads

John Doe (Admin) - 2500 Leads
Jane Smith (Senior Sales) - 1000 Leads
Jane Doe (Consultant) - 500 Leads

I want John Doe to be able to see all 4000 leads (not currently a problem)
I want Jane Smith to be able to see 3500 Leads 
I want Jane Doe to be able to see only 500 Leads

Currently the role hierarchy is set as John Doe (Admin) with Jane Smith (Senior Sales) under to the right and then Jane Doe (consultant) under to the right of Jane Smith.

John Doe
          Jane Smith
                     Jane Doe

Any help would be appreciated thanks!