How close can you get to him before he heads the other direction? Try getting close to him then turn your back to him and walk backwards the rest of the way to him. It has worked for me before on a horse that would let me get about 15' from him before he headed the other direction. With my back to him he didn't feel threatened or in jeopardy of being caught.
so, you've tried the "walking down a horse"? And you've done round pen work, getting him to turn and come to you? Could you do that, round pen work, and have a halter in your hand the whole time?
If I don't have a halter he'll do it right away.