A wearable computing system that includes a head-mounted display implements a gaze timer feature for enabling the user to temporarily extend the functionality of a handheld controller or other user input device. In one embodiment, when the user gazes at, or in the vicinity of, a handheld controller for a predetermined period of time, the functionality of one or more input elements (e.g., buttons) of the handheld controller is temporarily modified. For example, the function associated with a particular controller button may be modified to enable the user to open a particular menu using the button. The gaze timer feature may, for example, be used to augment the functionality of a handheld controller or other user input device during mixed reality and/or augmented reality sessions.