It's not easy to tell you how to configure it for a VPN in this response, but you would generally develop the application and WCF service locally using a localhost:[port] service. And then when you want to deploy it you would change the "localhost" to an IP or domain name.
In fact, it is more involved than that, but that's the general idea. You would really have to read the documentation (from various sources on the web) on the best method for your purpose.
I hope this helps.
King Wilder, Feb 27, 2011