For most drum rolls, I find that good drummers will actually enunciate every hit. So you could simulate a drum roll with your stick in the air without too much effort. Buzz rolls and drag rolls (i.e. when your stick is literally just bouncing in high frequency on the drum head) seem to be impossible to simulate without a rebound force. I imagine, though, that the software would pick up on you doing any kind of roll and try to pick a sensible frequency and go with it.