you could to it via custom field and add this to your themes functions file
Code:
function custom_more($more) {
global $post;
$mymore = get_post_meta($post->ID, 'moreoff', true);
if ($mymore == false) {
return '<a href="'. get_permalink($post->ID) . '">' . 'Read more...' . '</a>';
}
}
add_filter('excerpt_more', 'custom_more');
just add a custom field to the posts moreoff and set it to true, those posts will have no more link.
might be a plugin to do this, but i would do it this way.
hope this helps.