Redirect primary blog for subscribers

I've been needing help with this for the past week. Please help.

But I need help on how to implement this. Is there something I can download and use. I am having an issue with users going back to their correct back end. I want them to go to http://www.site.com/THEIRSITE/wp-admin
not
http://www.site.com/wp-admin

Please advise.

I've found these threads:
http://www.intechgrity.com/automatic-primary-site-in-wordpress-multisite-set-blog-creating-users-primary-creation/#

https://premium.wpmudev.org/forums/topic/multisite-variable-link-to-admin-panel