The creation of neutrally stable compliant mechanisms is a balancing act between knowledge on the system and the application of a stiffness countering prestress. This paper presents a novel prestressing method for polymeric compliant zero-stiffness mechanisms, utilizing stress relaxation as an actor for imprinting a permanent elevated internal stress state. The method in questiondoes not require a complex mechanical setup for application of the prestress. A sensitivity analysis is performed for the variables of relaxation time and imposed deformation. Two mechanisms with different origins for zero-stiffness behaviour are presented, and made neutrally stable. The simulations for one of the two examples, after correcting for a stretch in the force-displacement relation ship, match with the experimental results for both the variation in relaxation time and imposed deformation. For the second mechanism, the simulation for relaxation time matches that of the experiment, but for theimposed displacement this does not seem to be the case.