Connect to multiple database server by type of query (delete, insert, select, update)

I would like to ask one question with database connection in CodeIgniter 3.

I check in database configuration, it provide setting database connection values for specific environments by placing database.php such as:

PHP Code:

$db['default'] = array(
        'dsn'   => '',
        'hostname' => 'localhost',
        'username' => 'root',
        'password' => '',
        'database' => 'database_name',
        'dbdriver' => 'mysqli',
        'dbprefix' => '',
        'pconnect' => TRUE,
        'db_debug' => TRUE,
        'cache_on' => FALSE,
        'cachedir' => '',
        'char_set' => 'utf8',
        'dbcollat' => 'utf8_general_ci',
        'swap_pre' => '',
        'autoinit' => TRUE,
        'encrypt' => FALSE,
        'compress' => FALSE,
        'stricton' => FALSE,
        'failover' => array()
); 


But my requirement is separate query select, insert, delete and update to connect to server, for example, select.server.com, insert.server.com, delete.server.com and update.server.com respectively.

My question: how can I configure database connection depend one query type (insert, delete, update, select) in CodeIgniter 3?

Thanks.