a very low-tech solution: set a kind-of slow attack. holding the key for a short period of time (< the attack) gets you a "low velocity" sound because it doesn'

a very low-tech solution: set a kind-of slow attack. holding the key for a short period of time (< the attack) gets you a "low velocity" sound because it doesn't reach the maximum volume; longer periods (>= the attack) give you the full velocity. it's dumb but it works!