Link for user to unpublish post (status: draft)

I am using this function:

if(isset($_REQUEST['action']) && $_REQUEST['action']=='mypublish')
add_action('init','my_publish_draft');
function my_publish_draft(){
//Get the post's ID.
$post_id = (isset($_REQUEST['post']) ?  (int) $_REQUEST['post'] : 0);

//No post? Oh well..
if(empty($post_id))
return;

$nonce = $_REQUEST['_wpnonce'];

//Check nonce
if (! wp_verify_nonce($nonce,'my-publish-post_'.$post_id))
wp_die('Are you sure?'); 

//Check user permissions
if (!current_user_can('publish_posts'))
wp_die("You can't do that"); 

//Any other checks you may wish to perform..

//Publish post
$post = get_post($post_id,ARRAY_A);
$post['post_status'] ='publish';
wp_update_post($post);

//Redirect to published post
wp_redirect('/dashboard/');
exit;
}

And this code:

<?php
$status=get_post_status($upost->ID);
if ($status!='publish')
				$url=add_query_arg(array('action'=>'mypublish', 'post'=>$upost->ID),home_url());
echo  "<a href='" . wp_nonce_url($url, 'my-publish-post_' . $upost->ID) . "'>Publish</a>"; 

?>

To allow users to publish their posts via the front end of my site (theseattlevine.com/dashboard). I now want to give them an option to un-publish their posts (change them back to drafts).

Can anyone help me figure out how to do this?

Thanks!