gistfile1.aw

<?php
    public function isValid($values)
    {
        if (array_key_exists('already_customer', $values)
            && $values['already_customer'] == 'on') {
                $this->getElement('billingfirstname')->setRequired(false);
                $this->getElement('billinglastname')->setRequired(false);
                // ...
             }
        }

        return parent::isValid($values);
    }