Redirect login to original domain?

Hey I was wondering if there was an easy way to redirect the users from their mapped domain when logging in to their original domain.

We are using the option of “Redirect administration pages to site’s original domain (remote login disabled if this redirect is disabled)” but this doesn’t redirect the wp-login to the sites original domain.

Any idea on this? Thanks!

http://wordpress.org/plugins/wordpress-mu-domain-mapping/