Yes, the best way to get ghosts is to set them up to die as soon as the game starts. You can, for example, give a sim the 'on fire' moodlet, and let it run down to almost zero, so they die when you start the game for the first time. The same goes for drowning. Or make them really really old so that they will die within the first few game days. Basically any death that has a moodlet (starving is another one) you can do quite easily.