Automatic Domain Mapping

Is there a way for the domain mapping to be automatic for my customer? Meaning, they set up their site using the ProSites plugin and then they go somewhere and buy a domain name, choose domain mapping and enter the domain name and then go to where they bought the domain name and tell it to point to my IP address and that is all....?? I am finding that the only way I can get it to work is by adding the domain name to my hosting account. I am looking for a way for this to work without me having to do anything with it, is that possible?