We teach horses to neck rein with the reins in their normal position. We just use leg pressure and put the off rein against their neck. That way we aren't working on an accident by having the reins crossed if we need them. The horse learns to follow his head with the direct rein, move with the leg pressure and the neck pressure. All of it means turn and eventually any one of the three means turn. Working on this in the sage brush is good practice and training because they have to turn :) or plow through a 3' prickly sage brush.
That's what I've done with Bay when I've tried to work on it.... just add the neck rein to the direct rein on the other side... even one handed. I can slide the reins and give enough of each. Bay's just always been direct reined when it matters. I could get him to make gentle or obvious turns with a slack neck rein, but if he's got to do a 180 in the trail, or go some direction that isn't his first choice, I direct rein.
I think ecurbh has found Cyn to be more relaxed relatively slack and neck reining... having been started in Western Pleasure, I suppose that's her norm.
I've always ridden Bay with more contact with his snaffle Kimberwick.... but I'll have to be more slack with the new hackamore.