I did a back carry with two slings a few times, before I had a MT, because I am a terrible wrapper. I have to have two-shouldered carries, so two slings seemed good. I never did it much because dd doesn't like back carries, but it seemed like it would work well (once you get used to where to start the rings at so that they tighten into the right place). Although I had never seen that web page (thanks for the link!) and did it with both sets of rings in the corsage position. The way the maya page shows seems like it'd be easier to adjust. Let me know if you try it out!
