Multiple Networks Under 1 Domain

Is there any way to have multiple multisite networks operate under the same domain? Say we have a server/network in Los Angeles, and another in New York. And we want users to pick which server they sign up under. But we'd like them both to be under domain.com, so a site created on either one would be subdomain.domain.com. Of course we'd need a way to manage the hosts in our DNS records, and a way to synchronize the usernames so the same subdomain/username couldn't be used on both.

Is there any (reasonably easy) way to do this?