C# Decorator Class using Default Class Version of Method

How do you leave a method the same as the default implementation if trying to decorate a class?

For example I am trying to add a property to a IWebDriver interface of the WebDriver class.

i.e.

public class MyWebDriver : IWebDriver
{
    private IWebDriver _driver;
    internal string _currentTest { get; set; }

    internal MyWebDriver(IWebDriver driver)
    {
        _driver = driver;
    }
}

Visual Studio IntelliSense had me implement the class (or interface) with a bunch of 'throw new NotImplementedException(); as the method body for the default WebDriver class methods.

i.e.

public IWebElement FindElement(By by)
{
    throw new NotImplementedException();
}

My question is if I don't want to adjust the behavior of these methods at all how do I implement that? Do I just leave it all as that line in the body or do I have to for example (if this is the case how would it be done for the FindElement method w/ a return type and parameter?):

public string CurrentWindowHandle
{
    get
    {
        return _driver.CurrentWindowHandle;
    }
}

public ReadOnlyCollection<string> WindowHandles
{
    get
    {
        return _driver.WindowHandles;
    }
}

public void Close()
{
    _driver.Close();
}

public void Quit()
{
    _driver.Quit();
}

I am just trying to add a string variable to the IWebDriver interface to keep track of which test is running.