You can certainly set it up in an ethical way. For example, tell the subject that they have to find something as fast as they can. It could be a set of drawers and a large bin nearby. One could deduce their (admittedly sunk-cost biased) intuitive probabilities from where they start looking and when/​whether they switch from looking in the drawers to the bin. As described, this would not be easy or clean, but you can certainly modify the experiment to achieve both.
You can certainly set it up in an ethical way. For example, tell the subject that they have to find something as fast as they can. It could be a set of drawers and a large bin nearby. One could deduce their (admittedly sunk-cost biased) intuitive probabilities from where they start looking and when/​whether they switch from looking in the drawers to the bin. As described, this would not be easy or clean, but you can certainly modify the experiment to achieve both.