I'm on the knee-dragging side of the MC house, personally. So the issues on this side of the fence are more centered around so little rake
(24~ish degrees/sub-100mm trail on some bikes) that we run into the same problem from the other direction.... Regardless. I can *surely* appreciate a pimp ride.
Having said that, you might want to prep your client accordingly: Tell him to look up "Tankslapper" on YouTube...
Actually, you might want to grab some popcorn and do that anyhow!! Entertaining as hell to watch!
More seriously: If he does end up having a problem, a steering damper can help keep it under control... Wouldn't be pretty to have one hanging on the bike, tho...