I would take that rolling your hips idea with a grain of salt. Not everybody's back and pelvic anatomy is the same. It's kind of the same thing as suggesting you should have a flat back as opposed to an arched one. I feel a lot better arched, personally.

With the back pain you describe, I wonder if you're not trying to sit too far back. Have you tried having your saddle higher and bit more forward. The only time in my life I ever had back pain after riding was a few days about 10 years ago when I got carried away after reading some advice about pushing the saddle all the way back on its rails.