If at all possible, you should try to simulate a greenscreen affect by using a background that may not accomplish, but get very close, to being a solid color. You might be able to simulate this affect by placing the subject in front of a dark, shaded area while having enough light to pour on your subject. You may need to set the camera to a low exposure level. The wall of a building is also another possibility to investigate – you’ll have a harder time using a brick wall.
If the probability exists, you should definitely take advantage rather than tediously masking every single frame.
