How to create a login button for all my multisite users

Hello,

Currently when users sign up for a blog on my multisite install they receive and email from the Pro Sites plugin with their WP login URL, ex.theirblog.mymultisite.com/wp-login.

I'd like to add a login link to my main website that will allow all my users to simply sign in from there, instead of remembering the login url.

Is there a way to accomplish this?

Thanks,
Chris