Hi Dan,
In the current version there's no specific setting for only allowing a staff manager to book team members (but not allowing reservations). However, what I guess you could do is to set the reservation deadline to a large number of days (so that new reservations can't be made e.g. 90 days before the session). Once the deadline has occured, the manager will only be allowed to book team members, not make new reservations.
You could also use the same kind of logic for the "reservation cancellation days" (to automatically cancel non confirmed reservations).
//Rickard