Thanks go out to Sara Ford who blogged about this wonderful feature. If only I had known about this, oh, three years ago! :)
Here you go. Just copy/paste the following into a
.regfile and import it. You can change the colour (currently a very pale green) and at which column you want it to show (currently at 80). You can even add more columns apparently, but that's getting a little silly.
Windows Registry Editor Version 5.00