How is it not fair to him to be outside? Horses are livestock. No matter what you do you will never change that. Livestock stay outside. Yes we should supply them with a shelter that they are free to go in and out on there own. However, not keep them stalled for 12 hours at a time. I would go insane if I was locked in my bedroom for 12 hours.
Don't put nasty tasting stuff on the stall to prevent him from doing. A stalled horses that developes ulcers or prone to colic usually cribs because it "eases" them. If it didnt ease them they wouldnt do it. If you want to keep him stall then let him crib.
Our 26 yo only cribs indoors. Ulcer and Colic prone. He never sees the inside of stall. If he has to stay on stall rest, oh well....it aint going to happen. He can go in a large round pen or smaller paddock but not a stall.
Our 8yo mare will eat, literally eat, her way threw a stall wall. She is also ulcer prone and colic prone. Very nice mare but she has a busy body personality.
BOTH of these horses I would love to stall with my other guys. But, their personalities prevent that. Would they like to be out of the rain and wind and cold? Sure, why not. But stalling isnt the remedy to that. A run in shelter is. Just because its cold outside doesnt mean they are miserable. Just because its raining doesnt make them miserable. Yes they stand around with their heads hung lower and leg cocked back. Well, on a rainy day, so would I.
If you want to help him, just leave him alone. Don't feed him chemicals or bitter/spicy things that will ultimately give him ulcers. If he wants to crib indoors let him. If its that big of deal make a deal with you BO and set him up a special 1-2 acre paddock just for him.