You could try to update the php.ini settings that control session variables:
session.cookie_lifetime
session.gc_maxlifetime
You could try overwriting their values on the page itself, but it would probably have to appear on every page:
<?php
ini_set('session.cookie_maxlifetime', (3600*24*365));
ini_set('session.gc_maxlifetime', (3600*24*365));
?>