You can invite as supervisors entirely outside of approving hours or reviews. These company-wide admins or secondary supervisors will have access to apprentices in their organization but will receive zero notifications to approve.
Inviting a Supervisor
Simply go to the Supervisors tab, and click the orange button to invite a supervisor.
Indicate that you're inviting a Supervisor and assign their company. If they're not assigned to anyone as a reviewer (primary or otherwise), they'll simply see all of the apprentices in the organization when they login.
Inviting an Admin
Simply go to the Admin tab, and click the orange button to invite an admin.