Got the SSL to work using the V2 you posted about, however I've come across another issue
I'm using the Shopp ecommerce plugin and it uses Ajax to update the checkout page order values when you select a different delivery service. However, since I've been able to the page to show via Https, the ajax freezes whilst updating the page and I get the following error in Chrome Developer Tools console:
'XMLHttpRequest cannot load http://www.mysitedomain.co.uk/wp-admin/admin-ajax.php?action=shopp_ship_costs&method=Express+Delivery. Origin https://www.mysitedomain.co.uk is not allowed by Access-Control-Allow-Origin.'