Magento setting custome option sku for paypal and shopping cart

public function getOptionSku($product = null, $sku='')
    {
        $skuDelimiter = '-';
        if(empty($sku)){
            //$sku = $this->getProduct($product)->getData('sku');   //註釋掉
        }
        if ($optionIds = $this->getProduct($product)->getCustomOption('option_ids')) {
            foreach (explode(',', $optionIds->getValue()) as $optionId) {
                if ($option = $this->getProduct($product)->getOptionById($optionId)) {

                    $confItemOption = $this->getProduct($product)->getCustomOption('option_'.$optionId);

                    $group = $option->groupFactory($option->getType())
                        ->setOption($option)->setListener(new Varien_Object());
                    
                    if ($optionSku = $group->getOptionSku($confItemOption->getValue(), $skuDelimiter)) {
                        $sku = $optionSku;  // $sku .= $skuDelimiter . $optionSku;
                    }

                    if ($group->getListener()->getHasError()) {
                        $this->getProduct($product)
                                ->setHasError(true)
                                ->setMessage(
                                    $group->getListener()->getMessage()
                                );
                    }

                }
            }
        }
        return $sku;
    }

app/code/core/Mage/Catalog/Model/Product/Type  Abstract.php