How can I invoke a method of a private COM interface, defined in a base class, from a derived class?

For example, here is the COM interface, `IComInterface` (IDL):

```
[
    uuid(9AD16CCE-7588-486C-BC56-F3161FF92EF2),
    oleautomation
]
interface IComInterface: IUnknown
{
    HRESULT ComMethod([in] IUnknown* arg);
}

```

Here's the C# class `BaseClass` from `OldLibrary` assembly, which implements `IComInterface` like this (note the interface is declared as private):

```
// Assembly "OldLibrary"
public static class OldLibrary
{
    [ComImport(), Guid("9AD16CCE-7588-486C-BC56-F3161FF92EF2")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    private interface IComInterface
    {
        void ComMethod([In, MarshalAs(UnmanagedType.Interface)] object arg);
    }

    [ComVisible(true)]
    [ClassInterface(ClassInterfaceType.None)]
    public class BaseClass : IComInterface
    {
        void IComInterface.ComMethod(object arg)
        {
            Console.WriteLine("BaseClass.IComInterface.ComMethod");
        }
    }
}

```

Finally, here's an improved version, `ImprovedClass`, which derives from `BaseClass`, but declares and implement its own version of `IComInterface`, because the base's `OldLibrary.IComInterface` is inaccessible:

```
// Assembly "NewLibrary"
public static class NewLibrary
{
    [ComImport(), Guid("9AD16CCE-7588-486C-BC56-F3161FF92EF2")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    private interface IComInterface
    {
        void ComMethod([In, MarshalAs(UnmanagedType.Interface)] object arg);
    }

    [ComVisible(true)]
    [ClassInterface(ClassInterfaceType.None)]
    public class ImprovedClass : 
        OldLibrary.BaseClass, 
        IComInterface, 
        ICustomQueryInterface
    {
        // IComInterface
        void IComInterface.ComMethod(object arg)
        {
            Console.WriteLine("ImprovedClass.IComInterface.ComMethod");
            // How do I call base.ComMethod here, 
            // otherwise than via reflection?
        }

        // ICustomQueryInterface
        public CustomQueryInterfaceResult GetInterface(ref Guid iid, out IntPtr ppv)
        {
            if (iid == typeof(IComInterface).GUID)
            {
                ppv = Marshal.GetComInterfaceForObject(this, typeof(IComInterface), CustomQueryInterfaceMode.Ignore);
                return CustomQueryInterfaceResult.Handled;
            }
            ppv = IntPtr.Zero;
            return CustomQueryInterfaceResult.NotHandled;
        }   

    }
}

```

**How do I call `BaseClass.ComMethod` from `ImprovedClass.ComMethod` without reflection?**  
I could use reflection, but in the real use case `IComInterface` is a complex OLE interface with a number of members of complex signatures.

I thought that because both `BaseClass.IComInterface` and `ImprovedClass.IComInterface` are both COM interfaces with the same GUID and identical method signatures, and there's [COM Type Equivalence](http://msdn.microsoft.com/en-us/library/dd997297.aspx) in .NET 4.0+, so there has to be a way to do what I'm after without reflection.

Another requirement is that `ImprovedClass` has to be derived from `BaseClass`, because the C# client code expects an instance of `BaseClass`, which it passes to the COM client code. Thus, containment of `BaseClass` inside `ImprovedClass` is not an option.

**[EDITED]** A real-life scenario which involves deriving from [`WebBrowser`](http://msdn.microsoft.com/en-us/library/system.windows.forms.webbrowser%28v=vs.110%29.aspx) and [`WebBrowserSite`](http://msdn.microsoft.com/en-us/library/system.windows.forms.webbrowser.webbrowsersite%28v=vs.110%29.aspx) is described [here](https://stackoverflow.com/q/19717787/1768303).