A couple of suggestions:
1. Note the time he is sick and shorten the lesson to 10 minutes less the next time (to avoid any "I've been airborne for 40 minutes so it must be time to be sick" habits)
2. Let him fly the approach. After 4 lessons he should be capable of following your instructions and, if necessary, you can always take over at 100 feet if it gets a bit scary!
3. Try him with different situations - fly after eating, fly before eating etc
4. One of my students once cured this by chewing gum constantly
5. Head movements to a minimum, eyes on the horizon, lots of air in the cabin
If no change - some people find those wrist bands very effective (it may be mind over matter but who cares if it works?)
If not - he should consult his GP who may have some suggestions.
On top of all of this - just talk to your student about it. He probably feels very stressed about it on many levels (getting in the way of learning, embarrasment etc etc) so an open dialogue may ease his fears. He isn't the first and certainly won't be the last!