You will definitely need to create a promo code. DH panel --> Home --> Rewards --> Create Promo Code
You can give your friend $50 discount with some extra features like free domains, free unique IP address as long as the total discount is below $97.
Once you have the promo code ready, next will be to make sure your friend key in the promo code correctly when he signs up his plan.
$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