I've tried his method before without success. However, since i seem to have exhausted so many other ideas I've just started to give it another go. One observation I've made is that it seems i really do need to use his neutral grip in order to hit good shots with his half swing exercise. He advocates having the left thumb on top of the shaft and the creases between thumb & forefinger pointing in towards the body as opposed to at the right shoulder. Perhaps a tad controversial(?), but to be fair this gives me the conventional neutral 2 knuckle grip. With my more natural (for me) strong grip, all my shots with his half swing exercise were going low and left - makes sense i suppose, as with his hand release a strong grip would lead to a closed clubface at impact i guess.
So, using the markings on my grips on my ping i20 irons as a guide, i positioned my left thumb right down the centre of the grip at the range and did his half swing exercise. And with my PW and 8 iron i hit lots of really good ones, about 110yds and 130 yds respectively, very close to the full swing distance with good trajectory and accuracy too. It feels strange, but i am encouraged.
I should add that to help me do the half swing exercise correctly i used another drill from his DVD to familiarise myself with his half swing finish position - the one where from the address position you move your hips left, squeeze the clubhead into the ground and let it flip through into this half swing finish position.
BTW, this is an excellent forum!