Custom Role for a user to access the PM/Project Administrators to create the Billing Events

Summary:

We have a requirement to have the role to give access to Project Managers/Project Administrators to create the Billing Events, But That role should NOT allow the Project Managers/Project Administrators to access Generate the Invoices and Other Process and Administer Work Area like, Generate/Delete the Invoices and Manage Rate Schedules/Burden Schedules/TP Schedule.

We have tried with customizing the Project Billing Specialist Role and only adding the "Manage Project Billing Event" Privilege, but it is automatically inheriting the Manage Project Invoice privileges which we don't expect should be there.

Could you please suggest the way around that is it possible to have the only Manage Project Events Privilege to be given without access to Manage Project Invoices Process and Administer?