No, adding more will not help. And given what you describe, they should be separated ASAP or the loser will soon be dead.
We frequently read of having caves, plants, whatever to break up the sight, but that rarely solves the problem. Fish communicate via chemical pheromones and this alone can be highly stressful to a fish that factually is not wanted in the tank by the aggressor. In nature this is not a problem because the territory is defined and given the extent of the watercourse the submissive fish (for lack of a better term) can easily get away from the danger. In an aquarium this is not really possible. The dominant male is exercising his inherent right to set up his territory, but the submissive male (can be a female too) is prevented from taking the cue and leaving due to the space restriction.