こんなんでどうかな。

(defvar my-navi2ch-translate-url-regexp-list
'(("\\`http://203.192.159.253/" . "http://kanto.machi.to/")))

(defadvice navi2ch-article-select-current-link-url
(before my-translate-url-navi2ch-article-select-current-link-url activate)
(dolist (elt my-navi2ch-translate-url-regexp-list)
(catch :break
(when (string-match (car elt) url)
(setq url (replace-match (cdr elt) nil nil url))
(throw :break nil)))))