Trim your eyebrows and exercise the superior rectus muscles.
Seriously though, I have a fusion and two artificial discs and my neck extension is limited, so I know from this problem. I also know from long experience that staying low in the drops with weight back is the only safe way to descend fast, especially on bad pavement, of which there is a lot here. To augment the problem, I have deep-set eyes and I figure the overhang of my ugly skull costs me a few degrees of flexion.
I have actually considered looking into custom glasses with a weak prism insert at the top to help me get lower on the bike safely and comfortably, but I don't know if such a thing is even possible.