My concern would be that the whites contain a substantial portion of the (moderately low) % protein in an egg, while the yolk contains substantially all of the fats. Now because the egg yolk is nutrient dense compared to the albumin, the protein content as a % of weight actually comes up - almost 16%. But the fat content jumps to 26%Yes, that should work. I do not think there's any reason to limit the amount of yolk, as long as he continues to eat enough of the crumble every day too.
and the treat ratio would be 1 yolk per two birds daily.