Using a triangle neatly solves the problem and I have seen power supplies designed this way however ...
Floating dual tracking power supplies actually have 4 connections: positive, negative, common, and ground. My Tektronix PS503s have the floating outputs in line with common in the center so with a fixed width banana plug, I am limited to 20 volts. Maybe next time I rebuild them, I will swap the binding posts around so I have 20 or 40 volts available.