Because of the way BareMetal servers are set up they can't use the custom configuration option like most cloudboot hypervisors. Thankfully there is a workaround. The way is to manually add this configuration to the cloudboot image on the control server through ssh.
To do this ssh to the control server and then find this file:
It should be auto-created, but if not create it. Then make sure that it has executable permissions. Inside of that file just add what you would normally add to the custom config file for normal cloudboot Hypervisors. See here: https://onapp.zendesk.com/entries/23245878-Custom-Config-Examples