Well, I'm not talking about refactoring as in "a great adventure", but rather about a small and controlled change - spawning an empty subclass, then moving one method "as is" into that subclass.
Given the circumstances you describe, this may be dangerous too. For instance, someone may already have started calling methods by full name. Or, maybe, the setup() method shares some global variables with the rest of the code. Still my suggestion was nowhere near "rewriting all the code to make it better"!