Shoot your subjects with as much contrast as possible: ie, in dark clothing on a well lit white cyc with as little light as possible on the subject.
Then use AE to mask frame edges (garbage matte), adjust levels/contrast to darken the foreground more and lighten the background to pure white. Some manual rotoscoping may be required to fill in lighter spots on the subjects.
Alternately, shoot good quality green screen. Then key out the background and fill your subject with black.