Updating user profile on one mirror

I have a wordpress blog that is running on four mirrors. The installation is not in the root but in /blog and pointed by a sub domain (blog.example.org). Currently registration is running on only one under a sub domain.

How do i make sure that when someone logs in and points to profile.php it runs within the registration sub domain so that i do not have user details scattered all over the mirrors. I tried changing profile.php to (blog.example.org/wp-admin/profile.php) to open in the sub domain but after clicking you are redirected to a login page then it opens as (www.example.org/wp-admin/profile.php)