One thing that McHale talks about and that I have found out, is that the more the load is transferred to the middle of the hip belt (think just below both arm pits) instead of riding on your but, the better it rides and the less tight the belt needs to be.
Interesting. That got me brainstorming ways to transfer the load better to the sides, including some that resemble the "wing thing" idea. One idea that I think might work is to back the hip belt with something rigid in the vertical direction and flexible in the horizontal. Corrugated plastic (from political campaign signs) would fit the bill. I'd simply orient it with the channels running vertically and pre-crease every one so it'd be nice and flexible around my hips. Do you think it would be worth the weight?