Add custom data to user meta at registration

looks like you might be able to add checkout fields using a filter:

add_filter('woocommerce_checkout_fields', 'custom_checkout_fields');

function custom_checkout_fields($fields){
			$fields['account']['custom-field'] = array(
				'type' 			=> 'text',
				'label' 		=> __( 'Custom Field', 'woocommerce' ),
				'placeholder' 	=> _x( 'custom', 'placeholder', 'woocommerce' )
			);

return $fields;
}