The module also supports SASL authentication, it just isn't documented sadly. You'll need to run the following code:
<?php
$m = new Memcached();
$m->setOption(Memcached::OPT_BINARY_PROTOCOL, true);
$m->setSaslAuthData("user-1", "pass");
?>
You need to enable the "memcached.use_sasl = 1" ini option for memcached in the php.ini file.