[Spot] Keep all APs when translating LTL?

Hello, We are using the Python bindings in Spot to translate LTL to monitors, as described at https://spot.lrde.epita.fr/tut11.html. We have a question: Is it possible to set an option that will preserve all the atomic propositions, even when they cannot affect the automaton? For example, with the formula "Ga & Fb", the resulting monitor would not include "b". Is there a way to do this? Thanks, Dominick