Add supplemental address field 1 to BillingBlock.tpl
You have created a new template or customized one, right? Do you already have the address data available in your template? You can check this by making sure debugging is switched on in your environment and then access your BillingBlock.tpl but add &amp;smartyDebug=1 at the end of the url.
If not, you can use the API to retrieve the address data, assuming you know the contact id. In Smarty you can do:

{crmAPI var='result' entity='Address' action='get' q='civicrm/ajax/rest'}
{foreach from=$result.values item=Address}
  &lt;li&gt;{$Address.some_field}&lt;/li&gt;
{/foreach}


This will allow you to retrieve the supplemental address.