How do you suggest I hack MediaWiki to give partial disablement of interwiki links?

I have currently 2 (of an eventual 70+) languages setup:

http://en.chainki.org (with $wgHideInterlanguageLinks = true; in LocalSettings.php) http://fr.chainki.org (with $wgHideInterlanguageLinks = false; in LocalSetting.php - links to "English" work)

What I would like to do is display the interlanguage links only for those languages which are currently installed. Normally one would not have interlanguage links to languages which don't exist (duh!), but in this case, when I set up each new language the interlanguage links will then work.

Is there an easy way to only display links for certain languages?

I notice that there are classes like <li class="interwiki-es"> and I wonder if I could hack these classes to make the unwanted languages "invisible" (maybe white on white); if so, where and how?

Or any other suggestions?

Thanks!

Hugh