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, so a site created on either one would be 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?