Change Author link to be a subdomain

Hi,
I'm migrating a site to WPMU and my authors currently have a url of:
authorname.domainname.com

When we migrate to WPMU that changes to domainname.com/author/authorname

We need to set our site up so the authorname is a subdomain...

Each new WPMU blog will have it's own domainname, so this is 'theoretically' possible.

Can anyone point me in the direction to look for a solution?

Thanks!
Charly.