in theory you could chuck the steerer in a lathe and assuming you can get a cutter into the crown race area, just take it down (carefully) until it's 26.6 (to allow for press fitting). But in practice I can remember trying it once and the offset blades made for a dangerous situation once it was spinning...I decided not to risk injury or damaging my fork. Any LBS with a race milling tool can do it slowly and precisely without a lathe or milling machine...pretty cheap, too. Don't know enough to say if Campy made NR races for the JIS standard of 27mm, but if they didn't there is probably somebody who's discovered which JP brand 27 race is a good fit with a NR HS, personally I'd just get that crownrace milled and fergettaboutit.