as a person who has worked in a machine shop, I'll chip in with these comments:
1) you'd have to take apart the wheel down to the hub for this - I seriously doubt anyone would do this with the spokes and rim attached
2) its actually not -that- easy to put those fine pitch left hand threads on there
3) by the time you've paid the machinist $60 for the job you shoulda just bought a track hub from ebay
4) nice hubs probably have rolled threads which are quite a bit stronger than cut threads and you'd be hard pressed to find a machinist with the right threadforming tool to make the left hand rolled threads for you.

I say, nice idea but save your money and time