The rare kaon decay $K \to \pi \ell^+ \ell^-$ is highly suppressed within the Standard Model (SM) and is therefore an excellent probe for new physics. For this reason a robust SM value is needed. Since the latest physical point lattice calculation of this decay is limited by the stochastic estimation of quark loops, variance reduction techniques are required to move beyond this previous state-of-the-art calculation. We present the latest work utilising the split-even approach to compute this process on the lattice.