（临时？）我选择的解决方案如下：

使用show_in_menu 的参数register_post_type

。。。

// Sort the children of a given toplevel menu item
// Keep original order intact as much as possible, while
//  enforcing the [before => after] rules given by $force_order
function help_sort_submenu_items($toplevel_slug, $force_order) {
  global $submenu;

  $done = array();
  $hold = array();
  $newmenu = array();

  foreach ($submenu[$toplevel_slug] as $i => $item) {
    $force_after = array_search($item[2], $force_order);
    if ($force_after !== false && empty($done[$force_after])) {
      $hold[$item[2]] = $item;
    } else {
      $newmenu []= $item;
      $done[$item[2]] = true;

      $just_added_id = $item[2];
      while ($just_added_id = $force_order[$just_added_id]) {
        $next = $hold[$just_added_id];
        $newmenu []= $next;
        $done[$just_added_id] = true;
      }
    }
  }

  $submenu[$toplevel_slug] = $newmenu;
}

用法如下：

help_sort_submenu_items(\'my_plugin_toplevel_menu_item_slug\', array(
  \'submenu_page_with_this_slug_comes_before\' => \'submenu_page_with_this_slug\',
  \'another\' => \'rule\'
));