//add this code to your mobile site to link to the full site. (HTML)
<a href="example.com?view_full_site=true">View Full Site </a>


//code to add to your full site to show link back to mobile site if they came from the mobile site. (PHP)
<?php
if( isset( $_COOKIE['mobileesp_wp_full_site'] ) )
{
echo ("<a href="example.com?view_full_site=false">View Mobile Site </a>
}
?>