Question about Domain Names

I have WPMU setup under .com using sub directories. Manually through my registrar, I setup subdomains for anything I want on the .com domain to point to a blog on MU and use Domain Mapping with it and that seems to work fine.

Now, I want to allow users to create their blogs at their will but instead of using the .com domain name, I want their blogs created as subdomain.tbreak.me

How can I automate this? I know that using something like YAMM, I can manually add a new domain, but I would like the new .me domain to be the default for all new blogs and use a wildcard system in creating them