chosen_order.module

<?php
/**
 * Implements hook_form_alter().
 */
function chosen_order_form_alter(&$form, &$form_state, $form_id) {
  //|    Add some js to make multi-select chosen field sortable
  //|    Add a hidden field to store the sort order
  if ($form_state['#chosen_order'] && !$form_state['submitted']) {
    foreach ($form as $key => $field) {
      $key . '_order';
      if (strpos($key,'field_') === 0 && $field[LANGUAGE_NONE]['#chosen'] && $field[LANGUAGE_NONE]['#multiple']) {
        $form[$key . '_order'] = array(
          '#type' => 'hidden',
          '#attributes' => array(
            'class' => array(
              'field-type-chosen-order',
            ),
            'id' => 'edit_' . $key . '_' . LANGUAGE_NONE . '_chosen_order',
          ),
        );
        if (isset($field[LANGUAGE_NONE]['#default_value']) && !empty($field[LANGUAGE_NONE]['#default_value']) && is_array($field[LANGUAGE_NONE]['#default_value'])) {
          $form[$key . '_order']['#default_value'] = implode(',', $field[LANGUAGE_NONE]['#default_value']);
        }
      }
    }
  }
}

/**
 * Implements hook_field_widget_form_alter().
 */
function chosen_order_field_widget_form_alter(&$element, &$form_state, $context) {
  if ($element['#chosen'] && $element['#multiple']) {
    //|  Add sort js to all chosen multiple select widgets
    drupal_add_library('system', 'ui.sortable');
    drupal_add_js(drupal_get_path('module', 'chosen_order') . '/js/chosen_order_order.js');
    drupal_add_css(drupal_get_path('module', 'chosen_order') . '/css/chosen_order_order.css');
    //|  Add sort js to all chosen multiple select widgets
    $element['#element_validate'][] = 'chosen_order_form_chosen_field_validate_order';

    $form_state['#chosen_order'] = TRUE;
  }
}

function chosen_order_form_chosen_field_validate_order($element, &$form_state, $form) {
  $el_name = $element['#field_name'];
  $order_field_name = $el_name . '_order';

  //|  Get values and put in correctly formatted array
  $values = explode(',',$form_state['values'][$order_field_name]);
  if (isset($values) && is_array($values) && !empty($values)) {
    //|  Set value
    foreach ($values as $key => $value) {
      $values[$key] = array($element['#value_key'] => $value);
    }
    form_set_value(
      $form[$el_name],
      array(LANGUAGE_NONE => $values),
      $form_state);
  }
}