How can I get my horse over his fear of bridles?

I work with a horse who is terrified of the bridle going over his ears. He had a lot of problems when he first came to the stable, but this wasn't one of them. He slowly started becoming resistant to the bridle and is now panicky. A couple of people have tried to bridle him when he was tied to the fence, which just resulted in him snapping the lead rope and has only exacerbated the problem. He trusts me, so the stable owner has asked me to tackle this problem. I know he's not head shy as he loves having his head rubbed and he accepts the bit without a fuss, so that's not the problem either. He doesn't react negatively when I halter him and I have tried draping a rope around his head and ears and he is fine with that as well. I can rub his head and ears with the bridle or hackamore in my hand, but as soon as I make a move to put it over his head, he pulls back, raises his head so I can't reach it (he's half draft horse, so he's a BIG boy) and starts sweating. He's making huge strides in all of his other hang-ups, but I'm at a loss for this one. Any suggestions?