I'll have to look at my test box. I think I made this already! I was playing around when you first posted.
The only thing I'd say, though, is I did it just as direct template edits so if you want me to post here on how to do it, I will, but it won't be an actual add on you can just enable or disable. You may want to wait for someone who can do something more refined and professional.
I'm also just looking into ways that Google might be able to still see the content, even if it isn't readable by a human.