 <p>Derp. This works. </p> <pre><code>$address-&gt;setData('firstname', $this-&gt;getRequest()-&gt;getPost('billing_firstname')); $address-&gt;setData('lastname', $this-&gt;getRequest()-&gt;getPost('billing_lastname')); $address-&gt;setData('fax', $this-&gt;getRequest()-&gt;getPost('billing_fax')); </code></pre> <p>Anyone else needing this? </p> <p>Add form fields into <code>your/theme/template/persistent/forms/register.phtml</code><br> override <code>Mage_Customer_AccountController</code><br> <code>setData('key', 'value')</code> in <code>yourmodule/customer/controller/accountController.php :: createPostAction()</code> </p>