jQuery Grid Plugin - jqGrid

I have problem integration addional data into a formsubmit. I using the form whcih comes witzh jqgrid, not inline cell editing:

I have to add a addional values like referenkey from a parent object to the form submit:

thus I added

onclickSubmit:function(){return {item_id:};},
editData: {item_id:11},

according to the doc. Both should add a parameter 'utem_id' with value 11 to the postrequest. But it doesn't! 

Also I noticed that onclickSubmit doesn't get fired after clicking submit. I checked with

onclickSubmit:function(){alert('hi);},

Is this a bug? I working on that since hours...

jQuery("#itinerarygrid").jqGrid({
                url:'remote/product.cfc?method=getItineraries',
                editurl: 'remote/MyProxy.cfc?method=doProcess&event=admin.product.saveItinerary',
                onclickSubmit:function(){return {item_id:"11"};},
                datatype: 'json',
                mtype: 'POST',
                colNames:['ID','Day','Label','Description','Meals','From','To'],
                colModel :[
                  {name:'itinerary_id',index:'itinerary_id', hidden:true},
                  {name:'daynumber', index:'daynumber',width:25,align:'center', editable:true, edittype:'text',editrules:{number:true},editoptions:{size:6}},
                  {name:'label', index:'label', editable:true, edittype:'text',editoptions:{size:37}},
                  {name:'description', index:'description', editable:true, edittype:'textarea',editoptions: {rows:"8",cols:"33"}},                
                  {name:'meals', index:'meals',editable:true, edittype:'textarea'}         
                ],
                key:'itinerary_id',
                pager: '#ig_pager',
                rowNum:10,
                rowList:[10,20,30],
                sortname: 'daynumber',
                sortorder: 'asc',
                height:"auto",
                width:'680',
                viewrecords: true,
                jsonReader: {
                    repeatitems : false,
                    id: "itinerary_id"
                },
                ondblClickRow: function(rowid){
                    jQuery("#itinerarygrid").editGridRow( rowid);
                },
               
                imgpath: 'includes/styles/images',
                caption: 'Tours Itineraries'
              }).navGrid('#pager',{edit:true,add:true,del:true,search:false})
               
           
});