add_filter('post_type_link', 'k2_post_type_link', 1, 3);
function k2_post_type_link( $link, $post = 0 ) {
    $k2_post_types = array('columns', 'downloads', 'apps', 'cool_sites', 'tips', 'buying_buides');
    if(in_array($post->post_type, $k2_post_types)) {
        return home_url($post->post_type . '/' . $post->ID . '/' . $post->post_name);
    } else {
        return $link;
    }
}