Dedicated Customer Subinventory

Hi, We have a simple business requirement but there doesn't seems to be a perfect solution.

1) There is a class of customers let's say privileged customers.
2) Business wants to maintain a dedicated subinventory for some items for these customers let's say SUB1.
3) On sales order line: Requirement is to restrict all other customers by using any item's on-hand from SUB1.
4) Biggest problem is with ATP. When other customer's ATP should not see the on-hand from SUB1 and for Privileged customer's ATP should see the on-hand from SUB1.