This paper introduces a new control-on-request (COR) method that improves the capability of existing shared control interfaces. These COR enhanced interfaces allow users to request on-demand bursts of assistive computer control authority when manual / shared control tasks become too challenging. To enable the approach, we take advantage of the short duration of the desired control responses to derive an algebraic solution for the optimal switching control for differentiable nonlinear systems. These solutions minimize control authority while generating immediate and optimal degrees of improvement in system trajectories. The technique avoids the iterative constrained optimization required to derive traditional finite horizon optimal switching control solutions for nonlinear system and allows optimal control responses on time-frames otherwise infeasible. An interactive example illustrates how users can use COR interfaces to request real-time bursts of control assistance to help stabilize an unstable system.