Does anybody know of a MW extension that removes the rel="nofollow" attribute from external links after a set number of days? I want to encourage RichmondWiki.org users to contribute content and don't feel that it should be a "walled garden" to hog all of the PageRank. At the same time, I don't want to completely remove the nofollow from new links to discourage spamming and gratuitous links.

Thanks! andrew@richmondwiki.org