Passive, active and semi-active control have been extensively considered to improve the protection of base-isolated structures against earthquakes. This paper presents a strategy to apply control forces to the base of an isolated structure to enhance the performance of purely passive devices. The main feature is the simplicity in formulation, design and implementation. It is formulated as a static nonlinear function depending only on the base velocity. This function ensures energy dissipation capability with always bounded control force. The control is applied to a three-dimensional benchmark problem which is used by the structural control community as a state-of-the-art model for numerical experiments of seismic control attenuation. Several performance indices show that the proposed controller is efficient with a reasonable control effort.