Piano roll: different velocities triggering different sample

I have samples of pianos playing loudly and softly. How do I make it so when I have a low velocity on a note, it plays the quiet sample, and normal velocity is the louder sample? It doesn't necessarily have to be velocity. It would just be nice to be able to have this dynamic piano in one piano roll. Can I do this?

If you have DirectWave, I know you can do that ...