I have found with Africans it can be difficult if just adding one or two other fish. However if the tank is large enough you can stock heavier and sometimes this spreads aggression out. My biggest advice though is be prepared to move fish if the mixture is not working.
alsonif you go the route of stocking heavily be prepared for the extra work that comes with it. I have a 150 and am changing water every 3-5 days.