I haven't found any way to have aftertouch trigger any effects in the Piano. I don't see anything about it in the manual. Obviously real acoustic pianos don't support this, but one can hope that a virtual piano adds capabilities that are otherwise impossible with acoustic instruments. Pianoteq has a customizable curve for aftertouch (just as with velocity) and I find it's a wonderful way to add a little expressivity to my piano playing. It's weird if you overdo it, but I think a little adds some really nice element to a piano line without sounding too out of place.
So--someone please tell me if you know how to use aftertouch within the Piano, otherwise I hope this is added as a feature.
Note: I am pretty sure I could use my DAW to get some effect, but I think it would be better to do it in the Piano itself.