Open Haiku Stairs... look at the people who "climb" Diamond Head and then take a look at the people on Haiku Stairs. One look at,  or climbing 100 yards straight up the stairs,  will eliminate 80% of the people.  Haiku Stairs is at the top of the difficulty chart... very strenuous, even for the physically fit.  The crowds you anticipate will not be there... Open Haiku Stairs.  Or if you like, allow limited access... again, your anticipating problems that do not exist.