He is free ranged? He probably doesn't each much of the lay pellets then, correct? When I was able to free range any birds at all, they only at them first thing in the morning because they were hungry and then again in the evening before going to roost, they would fill up on them. So, not a huge part of the diet.
You could probably add liquid calcium to the water but I have no experience with it and therefore cannot guide you in that case at all.
Are your hens laying good hard shells on their eggs? They're getting enough calcium? There is a possibility that you could provide yogurt (plain and unsweetened) often. Its got a good calcium content to it and its really good for them in other ways too. That can get expensive.
Also, apparently meal worms are quite high in calcium but you'd have your whole flock on your lap for those!
If there is a way to separate him just for a few minutes to give him either mealworms or yogurt or both so that he is sure to get it all, that would be a possibility as well.