During gameplay, press TILDE (~) and then type "Cheat.GodMode()" to enable god mode. First, get two cloaking devices. Next, quicksave (press F5). Then, turn on both cloaking devices and leave them on. Now quickload (press F8). You will be cloaked until you reach a cinematic scene. (Note: This trick might not work in version 1.1.2.0 of the game.)