Getting hwnd for uxtheme.dll DrawThemeParentBackground from a Graphics object

I am dealing with some old drawing code used to draw parts of styled system controls in a WinFroms app. One of the core routines that does this work looks like the following:

private bool DrawTheme(Graphics graphics, XPThemeClasses themeClass, int themePart, int themeState, int x, int y, int width, int height)
{
    bool myResult;
    IntPtr myHdc = graphics.GetHdc();
    try
    {
        NativeMethods.RECT myRect = new NativeMethods.RECT(x, y, width, height);
        IntPtr myThemeData = GetThemeData(themeClass);
        if (NativeMethods.IsThemeBackgroundPartiallyTransparent(myThemeData, themePart, themeState))
        {
            IntPtr hwnd = NativeMethods.WindowFromDC(myHdc);
            int res = NativeMethods.DrawThemeParentBackground(hwnd, myHdc, ref myRect);
        }
        myResult = (0 <= NativeMethods.DrawThemeBackground(
          myThemeData,
          myHdc,
          themePart,
          themeState,
          ref myRect, ref myRect));
    }
    catch
    {
        myResult = false;
    }
    finally
    {
        graphics.ReleaseHdc(myHdc);
    }
    return myResult;
}

It turned out that the DrawThemeParentBackground function fails. It returns the error code 0x80070006 (E_HANDLE), which means 'Handle that is not valid'. It seems, this occurs because of the zero window handle retrieved with the prior WindowFromDC API call.

Is there a way to obtain the correct hwnd from the Graphics object passed to this function to pass it to DrawThemeParentBackground? I know I can pass the handle of the window to draw in from the outer calling code, but this would require rewriting of a big part of the infrastructure of this project. So I am searching for a simple solution of this problem without rewriting much code.