Way back in the day (30 or 40 years back), my Dad made up a transport belt. It wasn't much-- it was just a large leather belt with a large brass ring tacked on with a strip of leatherr and two rivets. He kept it all through his years as an investigator. While clearing out a storage unit of his recently, I saw it and asked if I could have it, since he's retired now. The other day, I put a large prisoner into it before putting him into my car. It's simple: you just buckle buckle behind him, with the belt passed through the brass ring in front. Then the handcuffs are passed through the brass ring, and his hands are cuffed in front. It's very safe, but FAR more comfortable to the prisoner. I am a fan of not hurting my prisoners.
A few days ago, I had a low-risk warrant to serve on my day off. I put on some blue jeans and a department polo shirt and an ID card, and put my pistol on my hip. I reached into my sock drawer, and got Dad's old sheep's leather 'cuff carrier from his days as an investigator, and put my cuffs into it, and looped it over my belt. It all went swimmingly, and the guy got booked in, in no time flat, without pain or injury.
Dad's old leather is still working.