The objective of our project was to develop a smartphone app for administering shorter ("modular") surveys. Given the paucity of research on this topic, we decided to use "co-design" techniques to generate design solutions. To implement these techniques, we recruited respondents in the survey target population to work in small groups and provide design ideas for the app. In this article, we present their input and examine whether we were successful in engaging them to contribute useful ideas. Although participation levels were uneven across the different groups, we found no evidence that group engagement was low overall or declined over the course of the sessions. In addition, the groups generated a diverse set of ideas, some of which informed the final app design. These findings underscore the feasibility of applying co-design principles to survey research, though further investigation is needed with different samples and design topics.