During my training I did a lot of back seat time during the summer during the afternoon in 172s. I was given a Reliefband (brand name) and it worked for me. It shocks your wrist and there's some scientific explanation to how it work. For me I usually went from on the verge of hurling to a mild head ache as soon as it started.
Of course, mythbusters 'busted' this one and we all know how perfectly valid their methods are!
I have had at least three students who have the same trouble you're having. One used the wrist band, the other two just got used to it over time.