A professional entity may render professional services only through its owners, managers, employees and agents who are duly licensed in accordance with the provisions of this state's licensing laws to render professional services; provided, however, this provision shall not be interpreted to include in the term “employee”, as used herein, clerks, secretaries, bookkeepers, technicians and other assistants who are not usually and ordinarily considered by custom and practice to be rendering professional services to the public for which a license is required.