I just gave this another thought recently (because my top competitor has this kinda package and is outmuscling me).
I want to create a special package... and when clients sign up to this package and pay, I will put them in a special client group... that will not pay for any hosting that they create (they will only pay for domain name).
I think this will emulate this setup well.
The only problem is that the client-group section is non-configurable. I would have put a 100% discount for this group if only I can limit the discount to hosting. How do I limit this discount to just hosting? (They will have to pay for stuff like DOmain names, Addons, so I dont want the discount to affect these).