Wordpress user registration only through CiviCRM
It looks like you could do the following:


Disable registrations in WordPress entirely (instructions in this SE question), OR
Add a WordPress hook implementation in a custom module which prevents WordPress registration via the regular methods (instructions in this SE question), then
Use that hook to ensure that only the CiviCRM registration flow is allowed. (Use variables unique to only the CiviCRM workflow or WordPress registration workflow to identify whether the user has followed the desired path, and reject otherwise.)