Work-Around for current_page_parent, current_page_ancestor in custom post type

<?php
class Webeo_Portfolio {
    function Webeo_Portfolio() {
        // ...
        add_action('template_redirect', array(&$this, 'fixWpQuery'));
        add_filter('wp_insert_post_data', array(&$this, 'savePostFilter'), 99);
    }

    function savePostFilter($data, $postarr = array()) {
        $data = (object) $data;

        if($data->post_type == 'portfolio' && $data->post_parent == 0) {
            // TODO: Automated search for PageID of portfolio-index page
            $data->post_parent = 4;
        }

        return (array) $data;
    }

    function fixWpQuery() {
        if(get_query_var('post_type') == 'portfolio') {
            global $wp_query;
            $wp_query->is_posts_page = true;
        }
    }

    // ...
}
?>