I must thoroughly agree with the use your legs while standing method.
This past weekend I was at an enduro race that had a lot of different type of terrain, some tight single track, some more open quad width areas, etc. The only constant was that is was semi sandy and every single straightaway was totally whooped out.
After getting my arse handed to me on 5 or 6 straightaways I started gripping with my legs. There were a couple sections I hit where I definitely hit the "sweet spot." My arms, legs, and body were in perfect position as I went over the whoops. The bike basically pivoted under me perfectly and I barely felt the whoops at all. Imagine riding one of those little toy horses rocking back and forth at slow speeds. It felt very natural and correct.
It didn't just happen either. Every time I hit a section I took a second or two and got my body into the correct position. I put the balls of my feet on the pegs, stuck my elbows out a bit, bent my knees, and gripped. I never looked down, nor did I really concentrate on the whoops immediately in front of my tire. I just kept my head up and eyes forward.