Writing third-party controls for Office 2007 so properties are visible in Office Design View mode

Question

I have a MS Word document in which are inserted a series of custom controls that maintain their own state and behaviors. I want the document designer to be able to set properties on these controls in design mode in Word (the designer doesn't have and shouldn't be required to have Visual Studio or be trusted with a compiler).

When I use Visual Studio Tools for Office (VSTO) to create a custom control, the public properties are available in Visual Studio Design Mode as expected, but upon inserting the custom controls into the document and going into Word Design Mode, the only visible properties are those of the ActiveX wrapper control that hosts the custom control in the document.

So I guess I want to develop a third-party control rather than a custom/user control. Any guidance on good tutorials on doing so?