spamming my own blog here but i wrote up a post on how to use VPNs as proxies on your webserver. there's not much info on it online
http://www.georgiecasey.com/2013/07/26/how-to-use-overplay-and-other-vpns-as-a-curl-proxy/
http://www.georgiecasey.com/2013/07/26/how-to-use-overplay-and-other-vpns-as-a-curl-proxy/