Case Management: Requirement for Cases to be Restricted to certain Case managers

Summary:

Our customer has a requirement for Cases that are related to HR employees to only be visible to specific Case Managers. We've tried creating a custom field and then configuring assignment rules against this to allocate these Cases to a specific Queue, however Oracle Support have advised us "automatic queue assignment for Case currently is not supported OOTB".

Even if we allocate Cases to a Queue manually, Case Manager not assigned to that Queue can still view and access the restricted Cases.

Does anyone have any suggestions or thoughts about how this requirement can be achieved?