Chad has been busily coding away and developed a cgi version of the subscribe to comments feature (originally developed in PHP). His is called "notifier". I plan on installing it here soon – but I have tested it on a "test" blog and it works great!! Installation is pretty easy (similar installation as MT-Blacklist).
I believe he has plans to include a feature that will import existing subscriptions, that'll probably be developed soon. If you have the (old) subscribe to comment script running and you want to change it to use this one – after following the installation instructions you only need to change the "action" attribute in your comments form tag. Change it back to the "default" – which if you're using MT 2.64 – you can just put this in:
action="<$MTCGIPath$><$MTCommentScript$>"
I should also add that Oscar Hills has also developed a similar plugin – but I haven't gotten my hands on it to try it out.
Thanks so much guys for answering my cry for help! 😀
(update: Just installed Chad's version here – let me know if you notice anything wacky)