I would think that would take some major tuning to get the maf to read right under boost. sounds like a tuning nightmare, but perhaps thats the reason turbos are so tough to tune..
Thing is, it doesn't seem to me that the lag is all that bad.. It isn't like you shift into 2nd on a racetrack and have to start at 2500 rpm or something.. when you shift from 6500 you are already at like 3500 or 4k and have boost.. the only advantage would be launching from a lower rpm or having a little more torque in a higher gear when cruising. The major downside would be the parasitic loss of running a smaller pulley..
Sold: 2006 GT Premium Vert, 5 spd, Tungsten Grey
New toy: 2001 Porshe Boxster S