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?
I don't think that would be as comfortable as you think. You want your belt to contour on your hips. I have been kicking around different wing ideas. I think the weight is worth it, while at the same time trying to minimize the weight increase as much as possible.
As far as sewing on the straping, my first one, I sewed through the padding. I had to do this by hand and used really heavy thread. It worked just fine. My second attempt, I used a heavier fabric and sewed directly to the outer fabric and then used spray adhesive to attach it to the foam, and then sewed a border and an inner fabric to the whole thing. I think it just matters what you are attaching the pack to. If the pack is attached to the webbing, then the padding itself isn't holding the weight, it is just padding the webbing.