How to enable STA in native C++ project?

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C++/CLI

C#

I have a C# class library (.dll). I want to use it from a unmanaged C++ application through a managed C++ static library. The C# dll has a form which contains a COM component(WebBrowser) which requires the current thread to be in Single Thread Apartment model. BUT the entry point is actually in the unmanaged C++ project, so I can't add any Thread attributes to my entry point. I have tried CoInitialize, but it did not work.

I then created a new thread and set its state to STA. Then the thread loads the form. This works correctly, but there comes an error in event handling.

...
// inside the constructor
m_view->DocumentCompleted += gcnew  WebBrowserDocumentCompletedEventHandler(this, &CLRWin::DocCompleted);
...
Void DocCompleted(Object ^s, WebBrowserDocumentCompletedEventArgs ^e)
{
     MessageBox::Show("Doc Completed");
     try
     {
          m_view->Document->MouseDown += gcnew HtmlElementEventHandler(this, &CLRWin::MouseEvt);
     }
     catch (Exception ^exc)
     {
        MessageBox::Show(exc->Message + " in object " + exc->Source);
     }     
}

The message box displays "Specified cast is not valid. in object System.Windows.Forms". The above code works perfectly in a CLR Application without any separate thread(but with STAThread attribute).

Also, I don't want to create a separate thread for this purpose.

I don't want to turn on Common Language Runtime support in my CLR project for many reasons.

Is there a way in native C++, to set the current thread's model to STA?

Thanks in advance.