Display Two Columns In A Listbox

I have a dropdown list in my view, it is populating from driver_master table, driver_master table contains first_name, last_name,driver_id etc., I want to show the first_name and last_name as display text and driver_id as value in list, I want to display driver_id as value and first_name,last_name as display text.I done the following method but still i did not get the result.

In Model:

function getFullName()
{
return $this->first_name.' '.$this->last_name;
}

function getDrivers()
{
$drivers = driverMaster::model()->findAll();
$list = CHtml::listData($drivers, 'driver_id', 'fullName');
return $list;
}

In View:

echo $form->dropDownList($model,'driver_id',$model->getDrivers());


i am getting the driver_id but i could not get first_name & last_name