I was looking into this a few weeks back and there seemed to be a flaw in the original setup as proposed in the OP here. After some time I came up with this:

https://gist.github.com/AdamISZ/350bb4038834019eb0c06ec69446aec9

(It links at the top to a (apologies, poorly formatted) schematic; the last part of which has a diagram which may be a useful aid to understanding).

Would appreciate thoughts, a couple of people looked at it, so far comments included possibly replacing CLTV with CSV.