Don't use kill order when doing barb trial during Meng Huo event. This will make you kill slower and get more duels. Number of killing will still remain at 400 million regardless of whether you use kill order or not. It just end faster if use kill orders. Same goes for Assiege (but I don't think anyone will be willing to do that due to competition for reward).
PS : only works if people in your country all cooperate and don't use kill orders, otherwise ignore the above.