How do I get the Membership Pro 2 registration to create a new subdomain site?

I'm setup and able to create a new *subdomain site from the root domains admin dashboard eg ( Problem is that when a new user registers through the Membership 2 registration only a subsite account is created eg ( What I need it to do is create a subdomain eg ( How would I go about doing this? I've searched for the solution on here with no luck.

Much appreciated,