Create type that implements internal interface

Question

Suppose I have assembly that declares internal interface IInternalInterface. I have no access to code of this assembly and I can't change it. How can I create my own implementation of IInternalInterface?

Why I need this: the assembly contains the class with list of IInternalInterface implementers and my goal is to add my own implementation there.

Answer 1

It is possible using remoting proxy.
Note that my answer is just a quick sketch and might need to be improved further.

internal interface IInternalInterface {
    void SayHello();
}

// --------------------------------------------------------------
// in another assembly
public class ImplementationProxy : RealProxy, IRemotingTypeInfo {
    private readonly MethodInfo method;

    public ImplementationProxy(MethodInfo method) 
        : base(typeof(ContextBoundObject))
    {
        this.method = method;
    }

    public override IMessage Invoke(IMessage msg) {
        if (!(msg is IMethodCallMessage))
            throw new NotSupportedException();

        var call = (IMethodCallMessage)msg;
        if (call.MethodBase != this.method)
            throw new NotSupportedException();

        Console.WriteLine("Hi from internals!");
        return new ReturnMessage(null, null, 0, call.LogicalCallContext, call);
    }

    public bool CanCastTo(Type fromType, object o)
    {
        return fromType == method.DeclaringType;
    }

    public string TypeName
    {
        get { return this.GetType().Name; }
        set { }
    }
}