Nodereference widget new type checkboxes

Hi,
First of all I want to excuse my bad english and the fact that I didn't know in which Component I should post my request. So is there a way that I can make node references as checkboxes? There is only a select list, And I had to modify the nodereference.module to have checkboxes. That's not good in case of an update, anyway here is the code how i did it:
Greetings

/**
 * Implementation of hook_widget_info().
 */
function nodereference_widget_info() {
  return array(
    'nodereference_select' => array(
      'label' => t('Select List'),
      'field types' => array('nodereference'),
    ),
    'nodereference_autocomplete' => array(
      'label' => t('Autocomplete Text Field'),
      'field types' => array('nodereference'),
    ),    
	'nodereference_checkboxes' => array(
      'label' => t('Checkboxes'),
      'field types' => array('nodereference'),
    ),
  );
}

/**
 * Implementation of hook_widget().
 */
function nodereference_widget($op, &$node, $field, &$items) {
  if ($field['widget']['type'] == 'nodereference_select') {
    switch ($op) {
      case 'prepare form values':
        $items_transposed = content_transpose_array_rows_cols($items);
        $items['default nids'] = $items_transposed['nid'];
        break;

      case 'form':
        $form = array();

        $options = _nodereference_potential_references($field, TRUE);
        foreach ($options as $key => $value) {
          $options[$key] = _nodereference_item($field, $value, FALSE);
        }
        if (!$field['required']) {
          $options = array(0 => t('<none>')) + $options;
        }

        $form[$field['field_name']] = array('#tree' => TRUE);
        $form[$field['field_name']]['nids'] = array(
          '#type' => 'select',
          '#title' => t($field['widget']['label']),
          '#default_value' => $items['default nids'],
          '#multiple' => $field['multiple'],
          '#size' =>  $field['multiple'] ? min(count($options), 6) : 0,
          '#options' => $options,
          '#required' => $field['required'],
          '#description' => t($field['widget']['description']),
        );

        return $form;

      case 'process form values':
        if ($field['multiple']) {
          // if nothing selected, make it 'none'
          if (empty($items['nids'])) {
            $items['nids'] = array(0 => '0');
          }
          // drop the 'none' options if other items were also selected
          elseif (count($items['nids']) > 1) {
            unset($items['nids'][0]);
          }

          $items = array_values(content_transpose_array_rows_cols(array('nid' => $items['nids'])));
        }
        else {
          $items[0]['nid'] = $items['nids'];
        }
        // Remove the widget's data representation so it isn't saved.
        unset($items['nids']);
        foreach ($items as $delta => $item) {
          $items[$delta]['error_field'] =  $field['field_name'] .'][nids';
        }
    }
  }
  elseif ($field['widget']['type'] == 'nodereference_checkboxes') {
    switch ($op) {
      case 'prepare form values':
        $items_transposed = content_transpose_array_rows_cols($items);
        $items['default nids'] = $items_transposed['nid'];
        break;

      case 'form':
        $form = array();

        $options = _nodereference_potential_references($field, TRUE);
        foreach ($options as $key => $value) {
          $options[$key] = _nodereference_item($field, $value, FALSE);
        }

        $form[$field['field_name']] = array('#tree' => TRUE);
        $form[$field['field_name']]['nids'] = array(
          '#type' => 'checkboxes',
          '#title' => t($field['widget']['label']),
          '#default_value' => $items['default nids'],
          '#multiple' => $field['multiple'],
          '#size' =>  $field['multiple'] ? min(count($options), 6) : 0,
          '#options' => $options,
          '#required' => $field['required'],
          '#description' => t($field['widget']['description']),
        );

        return $form;

      case 'process form values':
        if ($field['multiple']) {
          // if nothing selected, make it 'none'
          if (empty($items['nids'])) {
            $items['nids'] = array(0 => '0');
          }
          // drop the 'none' options if other items were also selected
          elseif (count($items['nids']) > 1) {
            unset($items['nids'][0]);
          }

          $items = array_values(content_transpose_array_rows_cols(array('nid' => $items['nids'])));
        }
        else {
          $items[0]['nid'] = $items['nids'];
        }
        // Remove the widget's data representation so it isn't saved.
        unset($items['nids']);
        foreach ($items as $delta => $item) {
          $items[$delta]['error_field'] =  $field['field_name'] .'][nids';
        }
    }
  }
  else {
    switch ($op) {
...