Hi Smeg! Love your Profile picture :D
For a horse that isn't treat inspired, you could try clicker training. I'm also going to write a post very soon on how to show a horse how to release pent up tension, by a simple lower jaw and TMJ exercise. You can find your horse's sweet spot, sometimes a point at the poll, or a scratch at the wither, which makes your horse feel much better than giving a treat. A gentle stroke at his 'sweet spot' will be enough positive reinforcement, as well as a kind word said with directed energy. A horse has a huge Torus field and can pick up on our energy very easily, so think good thoughts and send those vibes his way; he will know your intent and respond.