Use 2 of the 'Adjustable Angle Hinge' to make a single diagonal across the rectangle.

At the midsection of the diagonal, install an 'Adjustable 180 degree' along with two more of the adjustable angles in each corner.

Would that approximate it? Sorry I'm not better at ascii art.

https://makerpipe.com/collections/modular-pipe-fittings/prod...

I am just wrong due to incomplete info. The page I originally clicked on only had about half of the full catalog on it, and the way it was constructed I presumed it to be exhaustive.

There’s a 180° adjustable fitting that does exactly what I described, as a sibling to the link you provided.