This is some what of a glitch, and may not work for you, but I did it once and it was pretty cool. In the level where in the beginning you are running from the Smiths in that heap of a church, well at some point you will be standing on the edge of a building, if you do, look around on the tops of buildings with your sniper rifle, if you have one. Somewhere to the left on top of a big building, You might see Ghost, just standing around, you can shoot him dead if you want, it will not disrupt your game play. Enjoy.