This paper presents a novel prestressing method for polymeric compliant zero-stiffness mechanisms to obtain neutral stability. The method utilizes stress relaxation as an actor for imprinting a permanent elevated internal stress state. The method in question does not require a complex mechanical setup for application of the prestress. An existing zero-torsional stiffness mechanism is presented as a case study to demonstrate the working principle. Simulations have been performed and experimentally validated to present how stress relaxation can induce neutrally stable behavior in zero-stiffness compliant mechanisms. A sensitivity analysis is performed for the relaxation time to see its influence on the shift of the moment-angular deflection curve.