John,  I join you in this quest as I seek a MIDI solution for remote
controlled acoustic pianos and other devices.  At one time I had
information to MIDIfy such instruments with devices fitted above the
keys to trigger electronic "fingers" as you mention, with or without
pneumatic triggering, but have been unsuccessful retrieving it.

My current pneumatic player grand piano restoration uses e-valves
( http://members.shaw.ca/smythe/e-valves.htm ) but I'd really like
something for devices akin to what you seem to want.  I have an
harpsichord and seeking a plucked harp I would really like to actuate
from MIDI commands.

Paul Kealy
http://www.StentorVox.com/