In this paper, we reflect on the design and deployment process of MAGICBoard, a public display deployed in a university setting that solicits the electronic votes and opinions of bystanders on trivial but amusing topics. We focus on the consequences of our design choices with respect to encouraging bystanders to interact with the public display. Bystanders are individuals around the large display who may never fully engage with the application itself, but are potential contributors to the system. Drawing on our recent experiences with MAGICBoard, we present a classification of bystanders, and then discuss three design themes relevant to the design of systems for bystander use: graduated proximal engagement, lowering barriers for interaction and supporting covert engagement.