I came up with this today, partly inspired by Jahfunk's 'SStart experiments:
1. Record a lengthy white noise loop from a synth (I used a 20 second sample from a Roland Juno 1).
2. Assign it to a Preset and switch on Non-transpose in Voice Tuning.
3. In cords, Krand1 > 'SStart +100%; Krand2 > Abs +20%; Abs > Pitch +100%
Sample Start randomization is to reduce the incidence of flanging when playing chords. However, Krand1 will occasionally pick two similar start points, so this is why I've added some pitch randomization on top. Absolute Value is used to invert the Krand2 negative values because transposing a white noise sample downwards causes it to get "duller", which we don't want.
All in all, it seems to work pretty well. You can splash about on the keyboard as much as you like and it sounds suitably... noisy.