Lithium - using find('list') with SQL's DISTINCT gives me an empty array

Question

I'm trying to use Lithiums list option with find() along with SQL's DISTINCT. I should get an array populated with values, instead, I'm getting an empty array.

This does make sense since I'm passing in the distinct fields as one string instead of an array of elements but I don't know how else to use DISTINCT in Lithium.

Some direction would be greatly appreciated. It may be valentines day but Lithium is not showing me too much love today :)

Model:

class ZipCodes extends \app\extensions\data\Model {

    protected $_meta = array(
        'key'   => 'zip_code_id',
        'title' => 'state_name'
    );

    protected $_schema = array(
        'state_name' => array('type' => 'varchar'),
        'StateFIPS'  => array('type' => 'varchar')
        //there are more fields in my table but I haven't defined the
        //rest in my model
    );
}

The add method in my controller

public function add()
{
    $zipcodes = Zipcodes::find('list', array(
            'fields'     => array('DISTINCT state_name'),
            'order'      => 'state_name ASC',
            'conditions' => array('state_name' => array('!=' => ''))
        )
    );
    return compact('zipcodes');
}