Decay, like anything else can be (from our subjective point of view) be slowed down by accelerating it away from us at speeds approaching that of light.

As far as the parent comment's implied question, "and is that useful for radioactive waste disposal?" the answer is a strong "no, there are far better uses for the energy required, within and outside of radioactive waste disposal", including using this energy instead of energy from the nuclear reactor that makes waste.