This may be too late but here's my two cents...
I had lesson on the same problem yesterday...I'm a pro and work with a lifetime member of the PGA (he's been doing it for 29 years!) He keeps it really simple...forget all that plane crap. He gave me a few thoughts that worked...1. Picture a medicine ball in your hands at address position and rotate. It's that simple, your forearms rotate the club is inside and the club is not closed (the toe is up). 2. He stood behind/beside me and with no club in my hand, I had to reach back with my left hand and give him 'five'. (same thing, it promotes good rotation and the clubhead is not closed) 3. Last but not least, for folks like myself who really take it outside with an closed clubface, he said to put the butt of the club in my right pocket. Don't forget to rotate your forearms!
OK one more thing...check your club head at address and your grip pressure. If the club is the slightest bit closed at address, you have no choice but to go outside on the way back. As for grip pressure, keep it light and try not to squeeze with your right thumb and index finger. I made the adjustment to let those two finger touch slightly now on my grip and it really helped. GOOD LUCK!!!