When I signed up I didn't immediately name any domain names and I was given a username.dreamhosters.com domain. I was able to install a Wordpress installation there.
Later I began moving my domains over and got them pointed where they need to.
A friend just signed up for Dreamhost but put her domain name in although she hasn't begun the registrar transfer. I wanted her to have a Wordpress installation she could add her content to, but it will only let her create with her domain name as part of the URL and she hasn't pointed her old registrar's name servers to dreamhost yet.
She doesn't want the domain name to point to the unfinished new site.
In order to work on the new site, we both need an address to go to her new Wordpress installation.
How is that accomplished?