Hmm. I just read Gilles description a little closer. For adjustable height J-cup, the idea of setting the J-cup into the post wouldn't work.
How about one of these at least?
http://www.homedepot.com/p/OWT-Ornam...FcJ4AQodx4sBtQ (wfs)
An offset bracket would also be moveable. Now we're getting into have a lot of stuff to move and adjust....