I don't know if this is what you are looking for, but I've always used powershell to do this. If you have a master list of your servers in a table somewhere, then it is really easy to grab those with powershell and register them in the CMS.

Here is a good article to get you started with doing this in powershell:

http://www.mssqltips.com/sqlservertip/2658/using-powershell-to-register-all-sql-instances-into-central-management-server/