ZendX autocomplete with a callback

Question

Hi

I am using ZendX autocomplete to populate a postcode field

the JSON objects returns looking like this

{"77424039":"Lonehill - Sandton - GTG"}

what I'd want to do is grab the 1st segment "77424039" and populate a hidden field while the second segment "Lonehill - Sandton - GTG" populates the actual field

I assume i can do this with a callback function ( this is documented in the Jquery UI manaul) but for the life of me I can't see how to assign one to the ZendX_jQuery form component

I've tried many permutations of the code below

$elem->setJQueryParam("url","/object/autoComplete/LOV/","select","function(event, ui)");