I have had male guppies just by themselves before and their fine. I have had no expereince with them being stressed or fighting with each other. I wouldn't see why you couldn't do that.
i have 3 male endler hybrids in my fathers tank (To stop the hybrids respawning) and they are really happy. They chase each other around, theres rarely any nipping, and they seem to be probably the happiest fish ive ever kept (except for the 1 male to 9 females i once had, which died from exhaustion i think lol 2 days after it was introduced)