/**
 * Form alter hook Callbacks and helpers
 */
function _mymodule_formalter_exported_filter(&$form) {
  $filter_id = 'workflow_node.sid'; //set this to the id of the filter. use print_r($form['view'][#value']->filter) to find the ID

  foreach($form['view']['#value']->filter as $filter) {
    if ($filter['field'] == $filter_id) {
      $only_these = $filter['value'];
      break;
    }
  } 

  foreach ($form['filter0']['#options'] as $key => $option) {
    if (in_array($key, $only_these)) {
     $options[$key] = $option;
    }
  }
  $form['filter0']['#options'] = $options;

  if(is_array($form['filter0']['#default_value'])) {
    $form['filter0']['#default_value'] = 40; //or any other value.
  }
}

callback in a form alter to enforce an exposed filter to use only the options set in filter. Works for selectlists only.

Form alter to force exposed views filters to fllow filter options

php, drupal

PHP