The described embodiments augment an activity performed in a first application at a source electronic device using a controller at a companion electronic device. The source electronic device receives controller information describing a controller that the activity performed in the first application accepts controller data from, determines a controller identifier for the controller information, and broadcasts a controller advertisement comprising the controller identifier. Upon receiving the controller advertisement, the companion electronic device determines whether a second application that can provide the controller data is available at the companion electronic device. If the second application is available, the companion electronic device establishes a cooperative-activity communication channel with the source electronic device. The companion electronic device uses the cooperative-activity communication channel to provide controller data to the source electronic device. The source electronic device provides the controller data to the first application to cause a corresponding action to be performed.