Actually, in the few years I've been breeding mollies...Bachelor groups actually do pretty well without females to fight over.
It depends on space and hiding. Those are the two biggest things. Say you want five boys...you will want at least a 25+ gallon tank, bigger is better, with a lot of plants and caves. If you can get a 30 gallon that'd be about perfect for five boys and some cories, kuhli loaches or other small, peaceful bottom-dwellers. You want at least 5-8 gallons per fish as a bare minimum, if they don't have the space, they may fight for it. Same if you had girls too, but it'll be worse with boys if you don't have the space. With proper space they wont fight so hard, many think with less space they wont fight as hard because they don't have room to do so, but this is false with mollies. The only time I ever had so much trouble with sparring males was when I QT'd three in a ten gallon for two weeks, right away fight, fight, fight, plus their bioload is very high and they don't go well in small spaces. I used my twenty gallon as my QT after and had no issues with that! lol I've rarely had issues with males anyways, it's females I tend to get aggression issues with...
There may be sparring, it happens. Boys will be boys, but without females to chase, their spars will likely be...half-er...yeah, they wont go full force. lol Why risk injury without any benefits? Fish aren't as dumb as people think...though there are that special...many. LOL
Anyways, yeah, a bachelor group should do just fine. You may have a problem male or two, and you'll want to remove those. Any who rip fins, you want them out or it actually could start a mess. But in all likelihood, they will just do mini-spars and get along alright, may even try to mate with each other(if that happens don't be fooled unless you're unsure if you really do have all males), since livebearers are always trying to mate, even out of species or with other males.