Nope. This has been discussed before. It is not possible.
The only thing you can control outside DH panel is to allow customers to configure their own email boxes.
$50 off and 3 free domains with code: [color=#CC0000]DH3[/color] [url=http://dreamhost.com/r.cgi?296804/signup|DH3]Sign Up NOW[/url] or More Codes Here