DisCoPar (Distributed Components for Participatory Campaigning) is a framework inspired by flow-based programming (FBP) that enables users to develop and deploy mobile apps for participatory sensing purposes. The high reconfigurability and reusability on different levels of the system ensures that DisCoPar can be used to design a large variety of mobile data gathering apps. In this paper, we focus on the mobile app designer of DisCoPar. Specifically, we discuss how FBP principles such as the component-based design enable flexible app-logic composition, and how the visual aspect of FBP provides an intuitive interface for end-users. We demonstrate these principles by presenting a fully functional participatory sensing app designed with DisCoPar.