After setting the following to "lock," it's still possible to create an 
identity of "unnamed" by selecting the "select identity" option.
Maybe I missed something instead???.....
// default identity
// Set locked to true if you don't want the users to have multiple 
identities.
$_prefs['default_identity'] = array(
    'value' => 0,
    'locked' => true,
    'shared' => true,
    'type' => 'implicit'
);