Hold Row At The Top Of Gridview

Hello!

Please help me, if anyone can. How to form dataprovider so that one of the row for output to gridview has always been at the top?

I have a list of items that I want to display in the table and one of those items is the default value, that is, when user add a new item to the table, info from default item will be copied to the initial values ​​of new item.
I would like to see this defult item displayed in the table always at top in any sorting.
To indicate the default item has a separate field in the table, named 'default_user'.

I try this code:

$dataProvider = new CActiveDataProvider($this, array(
                            'criteria'=>$criteria,
                            'sort'=>array(
                                'multiSort'=>true,
                                'attributes'=>array(
                                    'username' => array(
                                        'asc' => 'default_user = 1, username ASC',
                                        'desc' => 'default_user = 1, username DESC'
                                    ),
                                    'useremail' => array(
                                        'asc' => 'default_user = 1, useremail ASC',
                                        'desc' => 'default_user = 1, useremail DESC'
                                    ),
                                ),                            
                                'defaultOrder'=>array(
                                    'username'=>CSort::SORT_ASC,
                                    'default_user'=> 1,
                                ),
                            )
                        ));

But when I change sorting by name to DESC - defult user go to the bottom of gridview.

What I do wrong?

Thanks for any help