  It is proposed to compute matrix elements for the (unphysical) $K^0\pi^-\to
\pi^-$ transition to determine the next-to-leading order low energy constants
of the weak chiral Lagrangian. This allows us to evaluate $K\to(\pi\pi)_{I=0}$
decay amplitudes at this level of precision. This approach has several
significant advantages over the use of $K\to\pi\pi$ transitions, most notably
the elimination of s-channel disconnected diagrams and the use of fewer
inversions.
