From what I gather, there is no way for me to have manga processed without horizontal images being either split or rotated. I have a kobo forma which has a gyroscope and can do 90deg rotation. It would be optimal to leave horizntal images as they are, and then I can actually rotate my device to fit the content if I so desire, or zoom into it manually.

The logic for the splitting image is pretty convoluted, and seeing as I have little python experience I would really need a hand with getting that done.