The author describes the formulation, implementation and evaluation of a gamified methodological tool for the assessment of gesture control capability amongst a small group of musicians with quadriplegic cerebral palsy. The gesture capability tool formed part of a larger project: the design of a dynamic and multidimensional sound synthesis engine and hardware interface specifically for physically disabled musicians, and the project demanded an assessment of the dimensions of their preferred targeting control gesture. The gesture is ostensibly simplistic - striking a physical button or pad - and the author had prior anecdotal evidence that the control gesture might be more nuanced than presumed. The author has devised a system consisting of a simple hardware controller, dynamically mapped to a virtual physical object (in MaxMSP/Jitter multimedia software), both elements reflecting a `paddle-and-ball' game. The participants control the speed, height and stability of a vertically moving paddle (via the hardware controller) upon which rests a ball with virtual physical properties of mass, velocity and restitution. Gross motor function is assessed via the height, speed and bounce time of the ball, and fine motor control governs the speed and motion of the paddle. During the study, the participants quickly abandoned control of the explicit boundaries of the environment (hard or soft discrete strikes), in favour of the more physically demanding implicit dimension: the participants themselves challenged each other to `hold' the virtual paddle aloft allowing the ball to come to rest, thereby demonstrating a degree of fine motor control not previously observed or assessed by the author.