It might work if you specify both the custom NS names and the IP addresses (glue records) of our name servers at your registrar, but I'm not sure if this would work or not. You would need to create A records for the custom names in cpanel as well, pointed to the IPs of our name servers, so our system is aware of the names. I'm not sure whether cpanel will like it though when it goes to do name server checks. I'm not sure if it looks at the name, or at the ip of the server being used. If it's the name, this won't work for letting you create new domains. Officially, we don't support any configuration other than the one we list.