I grow leeks but not to show standard but have read in one of the gardening magazines that those people who grow them for exhibition fill long cardboard tubes with compost and put one leek seedling in each. (think the cardboard tubes are those used for Christmas wrapping paper.) I think they then bore large deep holes in the ground, place the cardboard rolls containing the seedling in, and backfill the holes with fine compost. The main soil will also have been heavily manured as leeks are heavy feeders. The cardboard roll will eventually dissolve over the growing season. I've never tried this. It seems too much like hard work to me but if you want to grow leeks which win prizes I guess you need to be prepared to go to these lengths. Perhaps if you Google "Growing Leeks for exhibiting" you might find more useful information.