  It is shown that the low energy coefficients of the next-to-leading order
(NLO) chiral perturbation theory needed to determine $\Delta I=1/2$,
$K\to\pi\pi$ decay amplitudes can be fixed by calculating $K\pi\to\pi$
amplitudes on lattice. Unlike using NLO $K\to\pi\pi$ amplitudes proposed by
Laiho and Soni, simulating $K\pi\to\pi$ transitions on lattice does not require
evaluations of s-channel disconnected diagrams which have been an obstacle in
practice.
