Enable Project Owners to change time entries from billable to non-billable (or vise versa)

It would be extremely helpful if Project Owners had the ability to change time entries on their projects from billable to non-billable (or vise versa). We use timesheet entries at the project level to determine what we are billing our clients and the Project Owners are the only ones who have authority to determine what is billable vs. non-billable. The current permission architecture creates a big headache for our agency operations.