If you have one, I'd say try it with a Pinto pulley so that is stays locked inside and can't slide out of position.
Another possibility is to read up on this thread, and find the post by yoyoman in which he shows a cheap, quick and dirty hardware setup that allows you to separate the Rope Wrench tether from the hitch. This would allow you to use the top hole of the triple attachment pulley for the tether alone. The entire thread is well worth reading, though.
http://www.treebuzz.com/forum/threads/hitch-independent-zk-2-tether.24766/
I don't know if moss is a member here or not; I could have sworn that he was, but just now when I tried to look him up in the member list, I could not find him. He's the guy that started the above linked thread, and his work is just unbelievably beautiful, and about as far from "quick and dirty" as it gets. Truly inspirational to look at.
I'm hoping to try out my yoyoman version tomorrow for the first time.
One more idea I have, from looking at your current setup, is that you could create a 2nd piece similar to the first, only put a small offset or dog-leg at the bottom where it connects to the triple attachment pulley. This would create in metal the same thing they do with cordage when they put two eyes at the bottom of the tether to make it compatible with the triple attachment pulley. You'd have to use small bolts or screws through the two halves of the metal tether to hold it together, maybe just two would do it.
The offset piece would mean that the tether would wrap around both sides of the pulley hole you want to use, and thereby lock the tether in place and make it so that it can't roll out of position.
I hope what I've written is understandable.
Tim