You can override the row click event handler. When click on a non-row area, the 'onClickRow' event is triggered with a '-1' parameter value passed to it.
(function($){
var clickHander = $.fn.datagrid.defaults.rowEvents.click;
$.fn.datagrid.defaults.rowEvents.click = function(e){
var tr = $(e.target).closest('tr.datagrid-row');
if (tr.length){
clickHander.call(this, e);
} else {
var dg = $(e.target).closest('div.datagrid-view').children('.datagrid-f');
var opts = dg.datagrid('options');
opts.onClickRow.call(dg[0], -1);
}
}
})(jQuery);
$(function(){
$('#dg').datagrid({
onClickRow: function(index,row){
console.log('onClickRow:'+index)
}
})
})