Allow multisite admins to log in with facebook

I am currently allowing users to register using facebook through my main network site. They can create a new site and access it (provided no domain is mapped to it yet)
However, once a custom domain is mapped, or they need to login through http://mysite.com/wp-login.php, that login page has no facebook support.

Is there any way to get the facebook open graph login to work on all the sites across the multisite by default using the network's facebook app?

Otherwise having facebook login on multisite with domain mapping is pretty useless since the key expires once the user tries to access his/her site and needs an username and password.