All you would need to make a proper support class would have buffs and debuffs with short timers that you need bring into play via a rotation similar to other classes. Off the top of my head, maybe having a time mage doing a constant rotation to gradually increase the combat speed of your party. Once you cap the attack/movement speed you move onto debuffing the mob if it isn't resistant and by the time you finish that move onto the next buff/debuff.