Automatically subscribe users to get email notifications of all comments after leaving a comment

Hey thanks for the great plugin. I've got a unique situation that requires us to automatically subscribe our users to get email notifications of all comments after leaving their comment to any post.

Kind of like the way "Notify of Follow-up Comments" is automatically enabled, without the user needing to take any action on their own, but I want them to be notified of ALL comments left after they leave their comment, whether as a direct reply to their comment or not.

I can modify the source code if someone can point me in the right direction.

Thanks!