jQuery Grid Plugin - jqGrid

I tried to pass in PostData that is calculated in runtime, but it doesnot work.

Something simple like this doesnot work($uid is not calculated in runtime):

$conn = new PDO(DB_DSN,DB_USER,DB_PASSWORD);
jqGridDB::query($conn,"SET NAMES utf8");
$grid = new jqGridRender($conn);
$query= 'SELECT employeename FROM employees where uid =?';
$grid->SelectCommand = $query;
$grid->dataType = 'json';

$uid=$_REQUEST['uid'];

$uid=($uid+2)/9;

$aux = array($uid);

// Let the grid create the model
$grid->setColModel(null, $aux);

// Set some grid options
$grid->setGridOptions(array(
    "rowNum"=>10,
    "height"=>"200″,
    "rowList"=>array(10,20,30),
    "sortname"=>"id",
   "postData"=>array("uid"=>$uid)
));

$grid->renderGrid('#grid','#pager',true, null, $aux, true,true);

Called using ?uid=16 in my URL. ((16+2)/9=2. When I used $uid=2 in replace of $uid=$uid/9+2 and it works fine but I need $uid to be calculated in run time -In the future, I need to encrypt the uid passed in as REQUEST parameter.).

Does JQGrid support real time calculation of the PostData, or is the PostData precalculated in someway since the above simple example doesnot work?

Thanks in advance.