I decided that I really did need to use a fully-dressed ghost. I went with a wedding effect (much more pathetic), and thought up a bit of story (it is easier for me to draw someone if I have given them an identity) but needed to test veils vs just hair, sleeves vs gloves, and get a sense of what sort of angle to go for. Once I knew that it was "curtains" for the bride (sniff), I knew where to place her... and that I'd have to postwork the photo to get a bit of lift from the real ones. More quick renders. Again, this does save time... if you are just going to show the face coming out of a wall, you don't need to check the clothes for poke-through). If you are going to blend with some element (dryad coming out of a tree, for example) you can test to see whether you want a front view or profile or whether a raised arm should echo a limb.