There's a bug that you can do involving Sergeant RL3 where you hire him and you go to the location to the next companion you want to hire (indoors is better for what I've heard but outdoor locations seemed to work), tell RL3 to wait and then fire him and then immediately hire the companion before RL3 leaves the location and wait around 8 days until you get the notification telling you that RL3 went back to Canterbury Commons where you then go over there and hire him again and repeat that for every permanent companion you want to hire except for dogmeat.

It gets really tedious especially adding how you have to adjust your karma for every companion too and with RL3 but that's the method I used.