Does anyone know how to assign a window region (SetWindowRgn or Control.Region in WinForms) without killing the theming in the non-client area?

For example, running the following generates a Windows 2000-style unthemed title bar, border, etc:

var form = new Form { Width=500, Height=500, BackColor = Color.Azure };
form.Text = "But soft, what light through yonder window breaks?";
var region = new Region (new Rectangle (Point.Empty, form.Size));
region.Exclude (new Rectangle (100, 100, 300, 300));
form.Region = region;
form.ShowDialog();

I'm guessing it's to do with this MSDN article which says:

As long as a window has a non-NULL region applied to it (SetWindowRgn), the UxTheme Manager assumes that this is a specialized window and the window will not use visual styles.

...hence UxThemes assumes it's a specialized window. Is there a way to tell the UxTheme Manager explicitly to theme a window?

windows winforms winapi
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