A display mode which overrides all surface materials, displaying them the same colour, does that for the glass as well, making it opaque.
SetObjDisplayMode for the Curtain Wall is viewport specific (which takes a lot of time to set up with many viewports). But moreover, Rhino (currently - I think it used to) doesn’t remember that setting from session to session so each object in each viewport has to be reset for every session.
Assigning the visibility of a curtain wall style’s “cell” component to a specific hidden layer causes only its lines to disappear, not its surfaces, in the above display mode. It remains opaque.