Well, one way to automatedly ensure someone controls all the subdomains a wildcard certificate gives would be to ask them to create dns records indicating that. Basically, the CA could say "you want *.example.com, then create a dns txt record at mzzafr2pr.example.com with the following text: F5cbUl7pL2JM7z and click here. We'll get back to you once we see the dns change propagate". If I can create a random subdomain they suggest within a wildcard range, that makes it almost certain I can create every subdomain.