I've started down the path of adding a 3-point harness to the rear of the LJ. I've started some rambling on the subect in another blog post. My intention is to install the harness so that my 6 year old daughter can us it. I don't do any crazy wheeling with her in the Jeep, but I still want her safe, and I figure this should do the trick.
I made this video once things were completed, Watching this, and reading this article, should give you a pretty good idea of how to get this all done. Enjoy!