As usual, it depends on how much time you have to invest in the task. If you just need double top menus - this is the <b>fastest</b> solution.
I agree it would be nice if eZ included the dynamic code or distributed its source. In place of that, my approach would be to create a template that generates the javascript to manage the menus. That type of code can be surprisingly easy to develop, if you have the time.
I'm going to watch this thread, hoping someone else posts the answer that I can copy.