Memcached Session Handler

Hello guys,
I want to change the session handler to memcached. Memcached is set up as system cache (works fine).
Now is the question for me how to change session handler?

in /protected/config/main.php I tried the following

'session' => array (
    'sessionName' => 'app_name',	 
    'class'=> 'CCacheHttpSession',
    'autoStart' => 'false',	 
    'cookieMode' => 'only',
    'savePath' => '/tmp/session',
    'timeout' => 300
),

I'm new to yiiframework and google and board search couldn't help me.