Space-multiplexed input allows the distribution of tasks across spatially separated input devices. In this paper, we present an empirical study that evaluates the practical applicability of space-multiplexed input to mouse-extended notebooks - a common configuration which integrates both a touchpad and an external mouse. Our study shows that (1) two-handed input can instantly be performed by subjects without significant loss in performance; (2) one-handed operation of space-multiplexed interfaces performs worse than time-multiplexed input; and (3) the touchpad can be faster to acquire than virtual handles of standard size.