[Plugin: Co-Authors Plus] delete one author from coauthors()

I am running both Co-Authors Plus and exec-php

I don’t want “Contributors” to be able to run PHP in their posts. But I want to add PHP to their post when approving it.

So I am adding my username (admin) as the first author and theirs as second and sometimes third author. But I don’t want “admin” to show as an author in the post on the site.

I add this to single.php
<?php coauthors()); ?>

and this is the output: admin, Maralyn D. Hill, and Norman E. Hill

Then I changed that to:

<?php
 $authors=str_replace('admin, ','', coauthors());
 echo $authors;
 ?>

and the output is: admin, Maralyn D. Hill, and Norman E. HillMaralyn D. Hill, and Norman E. Hill

Is there a simple way to keep the first original coauthors() from printing there. As you can see it prints with the admin included then a second time without the admin, which is what I want.
Why should this show anything on the page?

<?php
 $authors=str_replace('admin, ','', coauthors());
 ?>

It should just set a value to $authors but it shows on the post as this:

admin, Maralyn D. Hill, and Norman E. Hill

Thans,
Tim

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