[Context] Ethical requirements are a growing area of importance for software. Yet, when dealing with these types of requirements from users, the subject might not always give an accurate representation of their requirements, due to social factors. [Question/problem] Which methods can help mitigate social desirability when dealing with ethical requirements? [Principal ideas/results] This article proposes the usage of factorial survey experiments (FSE) to work around social desirability when working with ethical requirements. FSE works with vignettes, which the RE practitioner presents to the subject, and experimentally varies them to comprehend how the subject reacts to different stimuli. It enables quantitative analysis of requirements and their specifications, adding explainability and transparency to the RE process. [Contribution] This article describes how to use FSE for ethical requirements, and its advantages. We also give an example of application, for which we share preliminary results. Our work opens the discussion for a possible framework using FSE for ethical requirements.