How to revoke only the "Admin option" from a sysdba

 We are creating the sysdba accounts for all of us dba with our employee numbers so that the audit logs register our employee numbers.  I notice that the sysdba privileged has been granted but how to remove the "with admn option" from a sysdba?
What we want is, that only one sysdba from the Security Department will have the admin option, meaning he will be the only one in granting the sysdba role.