Sales manager sharing leads with subordinates

Sales manager sharing leads with subordinates

I'm having trouble getting sharing working the way I want it. I have a sales manager who is over two organizations. He's able to see all the leads of his subordinates.

The problem is that he has leads assigned to him. These leads are either in Region 1 or Region 2. He wants the sales people in Region 1 to see his leads in Region 1 and wants the sales people in Region 2 to see his leads in Region 2. However, he doesn't want the sales people in Region 1 to see the leads in Region 2 - and vice versa.

This seems like a common enough scenario, but since you can't assign a lead to a specific role or group, it does not appear possible. 

Has anyone come up with a way to do this? Or has anyone found a reasonable work around that doesn't include adding additional users?