izne

Meanwhile, I figured this out myself and here is my “rude” approach.
First I created the field in views/form.php like this:

<p>
                    <label for="sreg-vat">BTW</label>
                    <input type="text" name="billing[vat]" id="sreg-vat" value="<?php echo (isset($_POST['billing']['vat'])) ? $_POST['billing']['vat'] : ''; ?>" />
                </p>

Added a small function that writes the VAT…

private function addVAT($email, $vat = ''){
    /**
    * shoppregcust::addVAT()
    * by izne <me@izne.info>
    *
    * @param mixed $email
    * @param mixed $name
    * @return
    */
    global $wpdb;
	$id = $wpdb->get_var("SELECT id FROM wp_shopp_customer WHERE email = '".$email."'");
	   if($id){
	       $varr = array("vat" => "$vat");
	       $a = serialize($varr);
	       $sql = "
	       UPDATE wp_shopp_customer SET
	       <code>info</code> = '$a'
	       WHERE <code>id</code> = $id";
		  $wpdb->query($sql);
		  return 1;
		}

    return 0;
    }

… and used it after $shopp_customer->save(); like this:
$this->addVAT($customer_data['email'], $_POST['billing']['vat']);.
So far it looks like working for me.

Hey Steve,

THANKS!

I totally missed that variable name was incorrect.
I owe you a beer 🙂