Row level security for more than 1000 users

Hi,

We need to add more than 1000 users in manage permission, can anyone suggest a way to do it.

Basically we have 300 clients, which can have subclients , but each client should see its own/parent client data(forsubcllients)

So count of users will cross 1000 for sure.

Please guide as in how should we achieve this, we cannot filter at database level, as it will cause us to create 300 dashboards and 300 different set of views(not a good workaround), 

We are using role based in desktop, we have use table which sets [UserPrincipalName] = UserPrincipalName(), do i need to add all users in manager permission?If yes, please suggest if users are more than 1000.

Help!!!!

Thanks,

Honey Bhatia