Moral Dilemma: Irrational Preferences

From Stumbling On Happiness:

volunteers in one study were asked to submerge their hands in icy water (a common laboratory task that is quite painful but that causes no harm) while using an electronic rating scale to report their moment-to-moment discomfort. Every volunteer performed both a short trial and a long trial. On the short trial, the volunteers submerged their hand for sixty seconds in a water bath that was kept at a chilly fifty-seven degrees Fahrenheit. On the long trial, volunteers submerged their hand for ninety seconds in a water bath that was kept at a chilly fifty-seven degrees Fahrenheit for the first sixty seconds, then surreptitiously warmed to a not-quite-as-chilly fifty-nine degrees over the remaining thirty seconds. So the short trial consisted of sixty cold seconds, and the long trial consisted of the same sixty cold seconds with an additional thirty cool seconds...

... the volunteers' moment-to-moment reports revealed that they experienced equal discomfort for the first sixty seconds on both trials, but much more discomfort in the next thirty seconds if they kept their hand in the water (as they did on the long trial) than if they removed it (as they did on the short trial). On the other hand (sorry), when volunteers were later asked to remember their experience and say which trial had been more painful, they tended to say that the short trial had been more painful than the long one...

The fact that we often judge the pleasure of an experience by its ending can cause us to make some curious choices. For example, when the researchers who performed the cold-water study asked the volunteers which of the two trials they would prefer to repeat, 69 percent of the volunteers chose to repeat the long one - that is, the one that entailed an extra thirty seconds of pain.

Let's say that one of the people who did this experiment is forced to do one of these two trials again. He/she doesn't want to do either one, but they prefer the long one only because of this odd way our memory works. You are forced to choose one of the two for them. Which choice is the most ethical?

I don't know.