This can easily be done by yourself with two controllers.
Simply set up your match for 3 rounds (5 if combining with an achievement that requires 5), 5 minute time limit to ensure you have enough time. Make a match private split screen match for you and your dummy controller. You can also combine this method with the following achievements -
The Soul Hoarder achievement in F.E.A.R. 3 worth 60 pointsAttain a total of 25,000 Souls across all rounds of a Soul King match