I saw the picture you posted, and wondered the same thing. Since I haven't done it before, take this advice with a grain of salt. First mask off the grip and seat with masking tape. Next get use a rasp or double cut file to get the diameter close to of the handle. Then use 120 grit turning the grip by hand to bring it closer, and follow up with 220 or finer. Save some of the cork dust in case pits need to be filled & sanded.