Curve defined mobius square torus

So I’m modelling this square mobius torus shape. I’ve made it using a curve which is twisted 180 degrees and then bent around 360. I initially started with a simple square profile/cross section, but now I’m trying out version where the squares sides are curved. So I’ve figured out a way to model it using a bunch of modifiers, which I like as it allows me to tweak the cross section.

But what I’d like to try is to somehow define three separate cross sections: start, middle, end (the end gets joined back to the start at 180 deg). Then blend between them. Is there a way to use three curve shapes to do this?