One thing you could try is:
add an a4j:support which fires on the event your choice, and set reRender the components with it as you wish.
Try it, it seems to work, I tried it with action not with reRender, but the action method was called.
Ohh, to call it:
So you have to call the onblur event on the 'hidd' component, not on the a4j:support component!
of course! nice simple trick.