No work can be extracted from an isolated system in equilibrium with a single thermostat. Nevertheless there are systems, e.g. glass-forming liquids, where relaxation to the thermostat temperature is so slow that two different temperatures can be defined within the same system: the temperature of the thermostat and the effective temperature associated to the violation of the equilibrium fluctuation-dissipation ratio. Here we present the first numerical study which shows how is possible, by introducing a proper brownian motor, to extract work from the out-of-equilibrium regime of a glass-forming liquid.