How to get the new record ID, when adding a record to a multi-value custom field using the API?

Insert.php

<?php

/**
 * CustomValue.Insert API specification (optional)
 * This is used for documentation and validation.
 *
 * @param array $spec description of fields supported by this API call
 * @return void
 * @see http://wiki.civicrm.org/confluence/display/CRM/API+Architecture+Standards
 */
function _civicrm_api3_custom_value_insert_spec(&$spec) {
  $spec['entity_id'] = array(
    'title' => 'Entity ID',
    'type'  => CRM_Utils_Type::T_INT,
    'api.required' => 1,
  );
}

/**
 * CustomValue.Insert API
 *
 * @param array $params
 * @return array API result descriptor
 * @see civicrm_api3_create_success
 * @see civicrm_api3_create_error
 * @throws API_Exception
 */
function civicrm_api3_custom_value_insert($params) {
  $entityId = $params['entity_id'];

  foreach ($params as $cfKey => $cfValue) {
    if (strpos($cfKey, 'custom_') !== 0) {
      continue;
    }

    // Details of requested custom field and its group
    $dummy    = explode('_', $cfKey);
    $cfId     = $dummy[1];
    $cf       = civicrm_api3('CustomField', 'getsingle', array('id' => $cfId));
    $cfColumn = $cf['column_name'];
    $cgId     = $cf['custom_group_id'];
    $cg       = civicrm_api3('CustomGroup', 'getsingle', array('id' => $cgId));
    $cgTable  = $cg['table_name'];
    break;
  }

  // Validate params
  if (array_key_exists('id', $params)) {
    throw new API_Exception('This API is only for adding new records at the moment');
  }
  if (!$cg['is_multiple']) {
    throw new API_Exception('This API is for use with multiple-record custom groups only');
  }
  if (empty($entityId) || empty($cfId)) {
    throw new API_Exception('Entity ID and custom field must be specified');
  }
  if (empty($cfColumn) || empty($cgTable)) {
    throw new API_Exception('Error looking up details of custom field or custom group');
  }

  // Add the record, get its ID (what we're really interested in)
  // Data saved through core APIs is normally escaped in the DB, do that too
  $dao = CRM_Core_DAO::executeQuery("
    INSERT INTO `%0` (`entity_id`, `%1`) VALUES (%2, %3)
  ", array(
    array($cgTable,  'String', CRM_Core_DAO::QUERY_FORMAT_NO_QUOTES),
    array($cfColumn, 'String', CRM_Core_DAO::QUERY_FORMAT_NO_QUOTES),
    array($entityId, 'Int'),
    array(htmlentities($cfValue), 'String'),
  ));

  $cvId = CRM_Core_DAO::singleValueQuery("SELECT LAST_INSERT_ID()");

  // Replicate the hook params that come from a CustomValue.create
  $hookParams = array(array(
    'entity_id'       => $entityId,
    'value'           => $cfValue,
    'type'            => $cf['data_type'],
    'custom_field_id' => $cfId,
    'custom_group_id' => $cgId,
    'table_name'      => $cgTable,
    'column_name'     => $cfColumn,
    'is_multiple'     => $cg['is_multiple'],
  ));
  CRM_Utils_Hook::custom('create', $cgId, $entityId, $hookParams);

  // Replicate the output from something more like a create/setvalue
  $returnValues = array($cvId => array(
    'id'        => $cvId,
    'entity_id' => $entityId,
    $cfKey      => $cfValue,
    $cfKey . '_' . $cvId => $cfValue,
  ));
  return civicrm_api3_create_success($returnValues, $params, 'CustomValue', 'Insert');
}