Looking for a plugin, e.g. Subscribe To Comments

I’m using the “Subscribe To Comments plugin” on my blog and I’m very happy with it. When making a comment, the visitor can check a checkbox to receive an email if other comments to this post were made. For the moment I’m trying to increase the amount of Mail followers of my RSS feed and I was thinking that I could put a second checkbox in my commentarea with the following text: “Subscribe to the RSS feed and receive updates straight into your inbox”. When making a comment, the visitor has to type in his or her email address anyway.

Well, this is the idea I had, but I can’t find a plugin that will do this. Does anyone have an idea?