使用Compiled Lambda表達式而不是Activator.CreateInstance來初始化SoapHttpClientProtocol對象

我正在使用動態實例化SoapHttpClientProtocol對象（代理類）的代碼，並使用此對象來調用WS-Basic I Web Service。這是我的代碼的簡化版本：

public override object Call(Type callingObject,
string method, object[] methodParams, string URL)
{
    MethodInfo requestMethod = callingObject.GetMethod(method);

    //creates an instance of SoapHttpClientProtocol
    object instance = Activator.CreateInstance(callingObject);

    //sets the URL for the object that was just created 
    instance.GetType().InvokeMember("Url", 
    BindingFlags.Public | BindingFlags.Instance | BindingFlags.SetProperty, null,
    instance,
    new object[1] {URL});

    return requestMethod.Invoke(instance, methodParams); 
}

我注意到在某些情況下Activator.CreateInstance()調用會花費大量時間，所以我試圖通過使用lambda表達式來優化代碼：

public override object Call(Type callingObject,
string method, object[] methodParams, string URL)
{
    MethodInfo requestMethod = callingObject.GetMethod(method);

    //creates an instance of SoapHttpClientProtocol using compiled Lambda Expression
    ConstructorInfo constructorInfo = callingObject.GetConstructor(new Type[0]);
    object instance = Expression.Lambda(Expression.New(constructorInfo)).Compile();

    //sets the URL for the object that was just created 
    instance.GetType().InvokeMember("Url", 
    BindingFlags.Public | BindingFlags.Instance | BindingFlags.SetProperty, null,
    instance,
    new object[1] {URL});

    //calls the web service
    return requestMethod.Invoke(instance, methodParams); 
}

不幸的是，這段代碼不會創建一個callingObject類型的對象（而是返回一個Func<T>委託對象），因此當它嘗試在下一行設置Url時會引發異常：

System.MissingMethodException：嘗試訪問缺少的成員。

我在代碼中遺漏了什麼嗎？

謝謝！