The best method I found for this was a Team Objective server while being on the defending team on the map Stoneshill. When the attacking team has to push the battering ram towards the gate of the castle of the defending team there are two oil pots above the gate that the attacking team need to destroy with the ram.
Wait until the ram in pushed all the way to gate then use the pots whenever there are people near the ram. The best thing about this is that because of the ram being there, it forces people into the target area of the oil pots, all you need to do is get the timing right.