This is the way I did it. If you learn more, please share.
Use this code instead of the included function. The first will only work if memberName = realName and that is not always the case.
// Just return the user name
function ssi_getuser()
{
global $context, $user_settings;
if ($context['user']['is_guest'])
return "Guest";
else
return $user_settings['memberName'];
}