Add Organization Volunteers from the Opportunity Level

The ability to add volunteers to an opportunity who have accounts but have never signed up for an opportunity. Volunteers who have signed up to the organization but have never signed up for an event are not accessible to manually add to events. The options right now are "Add Volunteer" & "Import from .CSV" to add someone who has not made an account, and "Copy Volunteers from another Opportunity", but there is no "Add volunteers from Organization" or other method to capture folks that have signed up to the organization without registering for an event.