Don't you find the threaded rod "grates" against the sides of the hole it fits through? I would think you would be better off to grind of that section of threads.
Great idea and very simple, I am going to print this out to give to my friend that bought my WSM. I could see adapting it to a UDS but I use the size 13 method on mine, works like a charm.
There's not a whole lot of space between the grate and the base of the cooker. will you be able to get enough motion to make it worthwhile?
Come to think of it, that grate sits on the bolts sticking through from the legs, yes? They're not very long so if you shake it back and forth, won't you be risking it falling off of them?