function maintenance_exempt_form_system_site_maintenance_mode_alter(&$form, &$form_state) {
  $form['maintenance_exempt_ips'] = array(
    '#type' => 'textarea',
    '#title' => t('Exempt IPs'),
    '#default_value' => variable_get('maintenance_exempt_ips'),
    '#description' => t('Enter a newline-separated list of IP addresses who should be exempt from maintenance mode. <a href="@url">CIDR Notation</a> is allowed.', array('@url' => 'http://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing'))
  );
}