If he still wants to hold his poll too low then give him a bump bump with the whip or your leg to get him to raise it.
A more effective way to ask Beau to raise his head is to lift the rein so that the bit contacts the corner of the mouth, where it is soft and pliable. Since you want to affect his head, the rein is the proper tool. The hands control everything in front of the girth and the legs control everything behind the girth, according to the French philosophy from people like Phillipe Karl. The whip will ask him to move his shoulder and the leg will ask for more forward, both of which do not affect the height of head, and the head is what you want to change.
Don't use a steady pull on the rein when you lift it, but use a vibration or a give-and-take of the rein. The horse will respond better to an intermittent aid, as apposed to a constant aid. That applies to any aid, leg or hand.
This information comes from Carol McCardle, a clinician who is part of the Phillipe Karl School of Légereté, and with whom I have the wonderful opportunity to work with now. I've wanted to take lessons with her for years, and I'm finally able to do so.
I had the same problem with my Lusitano mare--bending at C3 rather than at the poll--and Carol asked me what I was doing to correct that. "Go more forward?" I answered. She was nice enough not to call that a lame brain idea, but offered the technique I just described: lift the head with a vibrating rein. And it worked! Athene raised her head happily and correctly.
As I just posted on GENERAL, Carol is one of the instructors who molded Adrienne Lyle, who was just selected for the 2012 Olympic dressage team. I am delighted to take lessons from Carol, though my dreams are not as lofty as an Olympic berth. "D