Has he had any other symptoms? I would assume there's been no trauma to the head?
Is he on any medication (or anything else) which could be causing it, I'm sure the doctors would have checked but just in case as it can be a common side effect of some medications (I had it with Dianette and while tolerating Sulfasalzine).
Is it definitely in his head rather then something related to his back and strain there?
He could try consulting an osteopath for some cranial osteopathy to see if that might help, check with his doctors first though.
Be gentle with him after the lumbar puncture, I had a hell of a headache before I had one but it carried it on for a while so may make him a bit worse.
I found this which may give you some info...
http://www.headaches.org/press/NHF_Press_Kits/ Press_Kits_-_The_Complete_Headache_Chart