Update: I have provided complete code example in answer below.

I have built my own little custom XML-RPC server, and since I'd like to keep things simple, on both server and client side, what I would like to accomplish is to create a simplest possible client (in C# preferably) using WCF.

Let's say that Contract for service exposed via XML-RPC is as follows:

[ServiceContract]
public interface IContract
{
    [OperationContract(Action="Ping")]
    string Ping(); // server returns back string "Pong"

    [OperationContract(Action="Echo")]
    string Echo(string message); // server echoes back whatever message is
}

So, there are two example methods, one without any arguments, and another with simple string argument, both returning strings (just for sake of example). Service is exposed via http.

Aaand, what's next? :)