[ComImport]
[Guid("3E68D4BD-7135-4D10-8018-9FB6D9F33FA1")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface IInitializeWithWindow
{
    void Initialize(IntPtr hwnd);
}

public void SetOwnerWindow(StoreContext context, Window window)
{
    var handle = new WindowInteropHelper(window).Handle;
    var initWindow = (IInitializeWithWindow)(object)context;
    initWindow.Initialize(handle);
}