Non prescribed sedation for clipping?

I'm looking for a sedation that I can use so I can clip my horse's head. He's fine with the rest of his body (he stood at the fence, untied, for 2 hours, without even batting an eye). Before I started his body I lent the clippers on his face while they were on and he was fine with them, but when I went to do his head after I'd done his body he just ripped his head in the air (he was over it). I don't really don't want to twitch him, because it doesn't work, he just rears, I want to do it very calmly. He's not a nervous, freaky or nutty horse, he's very calm, mellow and dopey, I reckon even something like Tryptophane might work (I'd never paste for a show because it would seriously send him to sleep). I'm wondering if anyone can recommend anything else, something that I don't have to get through the vet, otherwise I'll have to get Ace prescribed (our vet is really hard to get in touch with, even when it's something serious, like a horse has ripped a massive whole in his stomach). And please don't say don't bother doing his head, I think it looks really ugly, he's chestnut, his body's now really light blondey, palomino-y and his heads really dark orange chestnut (and really fluffy- ick!). I am going to re try it tomorrow and start with his head so he's not bored and completely over it, he might be fine then...

Thanks