3
Seems that GIJOE has just released a test version of the Sitemap module with this feature added.
The news for it:
http://www.peak.ne.jp/xoops/modules/news/article.php?storyid=55
To download it:
http://www.peak.ne.jp/xoops/modules/mydownloads/singlefile.php?cid=1&lid=44