This is a different approach to the perennial question about what a koi show is about.... the koi or the owners. I do not believe there is a truly fair way to award husbandry skills. For example, if Koikeeper A raises a grand Sakai nisai to be as good as it looked like it could become, and Koikeeper B raises a scrawny pond mutt tosai to be far better than anyone could have thought possible, which is more deserving of recognition? ...How do you know where they started? If you do not know what the koikeeper started with, then you are simply judging the koi.
Grow-out contests in which everyone gets a young fish from the same breeder and come back in a year to show them are a lot of fun. It might seem a way to judge husbandry on a level playing field, but it is not. There is tremendous genetic variation in 20 tosai as to future size potential, color quality, etc., etc. And what is the guideline? What if I grow my tosai to be the biggest, and a friend grows his to have the best Hi? What if my big mediocre-looking one is exactly what it should be, because it should not have its colors come together until year 4, while the one with great color has been made to peak too soon?
Perhaps take a "scientific" approach with a formula to give weight to how each person's koi placed in all categories... a type of sweepstakes award. Then divide by the number of entries each person had ... so, a person with 10 entries that all placed 3rd in their classes will win over the person who brought 5 entries, two of which were show stopping magnificent, but 3 of which placed 21st, 22nd and 23rd in the Kohaku class (which had 100 entries).

....never ending arguments, I'm sure.
I think you'll do best to stick to judging the koi. And to recognize husbandry, make a point on a personal level to tell someone that you think they did a great job raising a particular koi. That can mean a lot.