only show certian authors (certian roles) in a dropdown menu

Hi everyone,
Hope your all doing fine.

So I have a multi author website and the authors are set to only see and edit their own posts.

I want the admin of the site to be able to assign(append) a second author(judge) to the posts so that the appended author(judge) can be able to review the post and do the actions necessary.

So far I have built a custom field which displays the authors(judges) in a dropdown menu but I don’t know how to append the author(judge) to the post.

I have tried the Co-Author-Plus plugin and it works fine in appending the Author to the existing Author of the post but the only problem is that it displays all the users in an input field… I only want the Authors which I have with the role of judge to be displayed and I want them to be displayed in a dropdown menu.

I would really appreciate it if anyone could help me with this?

Regards!

http://wordpress.org/plugins/co-authors-plus/