I don't think you can... it can't hurt to ask support about it if you're really interested. But why do you care?
These are just the nameservers. No one using your website will ever encounter these addresses. They will only be visible if someone does a whois lookup on your domain.
If your issue is that you don't want people to be able to find out who's hosting you, just use the IP addresses of the nameservers instead of the full addresses:
That won't actually stop a tech-savvy person from figuring out your host, but it'll stop the average snoop.
Hey, wait -- do you mean "reseller client" when you say "friend"? Then I can understand why you might not like needing to tell them to give "dreamhost" addresses for nameservers....