I would not use food to do this but the basic idea I agree with. I use use my calm voice repeating the same phrase (mine is OK) and stroking his withers or neck.
From The Horse.com
By Nancy Diehl, VMD, MS
How can I teach my horse to let me put her blanket on over his head so I don’t have to unbuckle and buckle it each time?
A. Along with accepting garments that can or must go on or over the head, it’s a great idea for a horse to be relaxed and compliant with having things done around his head for many management reasons.
You have already heard me extolling the virtues of using positive reinforcement, and it will work well here too.
To start, you first train your horse to learn that he will be rewarded (usually with food) for doing the right thing. You can then link giving the reward—the primary reinforce—with what we call a secondary reinforcer, for example your voice saying “good” or a clicker. The horse learns that when you say “good” that means a reward is forthcoming and soon has the same meaning as a reward. And it is more of an instantaneous signal to the horse “just this second you did the right thing,” than you could ever give trying to quickly get a food reward into his mouth. This is especially important when you are not working close to his head or, like here, at some point you’ll have a blanket partly over his face!
This is in preparation to shaping your desired behavior, that is, the horse standing relaxed while you put something over his head. Shaping is rewarding each successive approximation to the ultimate desired behavior. So you start with the least objectionable thing for the horse, which might be even just approaching with the blanket. Give your reinforcers. Now do each next very small step in getting the blanket toward, on, and over his head, giving the reinforcer(s) for each small step the horse allows. Go back to the last successful step if he stops the process at any time by an avoidance behavior.
This can be done in a similar fashion using systematic desensitization. You begin with the blanket somewhere unobjectionable to the horse, maybe at his shoulder. Just touch or rub him with it there, then in very small steps move to rubbing it up closer and closer to and over his head. When you get to a resentful spot, go back to where he was comfortable and start again. Think of it as using the blanket to color in a picture of your horse, filling in every bit of his body. You want to do this slowly enough to avoid evoking any fear or resistance. You may also provide rewards during desensitization.
Either of these methods should get you where you want to be. You might want to do the whole procedure first with something less bulky and awkward to handle than a blanket, such as a large towel. Both will work best if done in a safe environment with the least restraint possible. Added restraint sometimes makes a frightening procedure even more so. I would posit that the positive reinforcement will get you there quicker and provide a foundation for learning other procedures. But desensitization is another good skill for you to learn to use to get your horse to accept touching with your hand or objects anywhere on his body.