In the same way we do now, using a system that would overlook people like Einstein, a patent clerk who hadn't finished his Ph.D., who published articles having no supporting empirical evidence. In fact, there was little concrete evidence supporting his ideas until 1919 (a solar eclipse), which would eliminate him from consideration for the "scientist" label in modern times.

Or Alfred Wegener, a mere meteorologist who had some crazy ideas about the continents floating around and who was shouted down by the real scientists during his lifetime (reliable evidence for plate tectonics only appeared long after his death).

Ironically enough, both stories support a foundational principle of science -- that evidence trumps eminence.