Associating custom submenu item with post type of top level menu item

You need the information about the current post type in your callback function that renders the submenu page output. And at this point there is a lot of information ready:

add_action( 'admin_menu', 'wpse_60730_demo_submenu' );

/**
 * Register sub menu pages.
 *
 * Note that get_current_screen() is still NULL now.
 *
 * @wp-hook admin_menu
 * @return void
 */
function wpse_60730_demo_submenu()
{
    // get public post types
    $post_types = get_post_types( array ( 'public' => TRUE ) );

    foreach ( $post_types as $post_type )
    {
        add_submenu_page(
            "edit.php?post_type=$post_type",
            "Extra $post_type", // this should be made translatable
            "Extra $post_type", // this too
            "edit_{$post_type}s",
            "order-$post_type",
            'wpse_60730_demo_callback'
        );
    }
}
/**
 * Render the sub menu page output.
 *
 * All information is set now.
 *
 * @return void
 */
function wpse_60730_demo_callback()
{
    $screen = get_current_screen();
    global $typenow, $parent_file;
    print "<pre>get_current_screen()\n" . htmlspecialchars( print_r( $screen, TRUE ) ) . '</pre><hr>';
    print "<pre>\$typenow: " . htmlspecialchars( print_r( $typenow, TRUE ) ) . '</pre><hr>';
    print "<pre>\$parent_file: " . htmlspecialchars( print_r( $parent_file, TRUE ) ) . '</pre>';
}

Result