Easy boosting method:
Host a custom match with a minimun of 5 players, in the match settings enable max 2 traitors, min 2 traitors and most important Survivors Win when all traitors are dead.
Once everyone is loaded, everyone exits the cabin and the chosen survivor starts wailing on the first traitor and kills him/her, (bonus double chievo is to swap the traitor´s clothes) then kill the second traitor for an early survivor win.
Rinse and repeat for all boosters.