This is a missing feature and is a must since there are a few features we can offer a customer who is only registering a domain (like configure microsoft live domains or google apps).

This domain addons might have the same features as the product addons (free, setup, recurrent, and have them billed with the domain renew with prorate in case they are ordered later) with the hability to configure the existing ones so instead of going to the registrar we would be able to manage them.