If you're using self-hosting, then you can specify the base address in the constructor of the ServiceHost
class:
Uri baseAddress = new Uri("http://........");
ServiceHost host = new ServiceHost(typeof(YourServiceClass), baseAddress);
With IIS, things get a bit trickier.... you might be able to provide a custom factory to create your service host - but that seems like a whole lot of work. In addition, with IIS, the virtual directory where your *.svc
file exists really dictates the URL of your service - so providing a base address really isn't of much value.