Easy. I did it.
use matrix ita to specify booking code X on flight JL in business, departure dates within the limits in the blog post, make them +-2 days, and search JFK-TYO.
note down or screenshot when the dates are available.
then, repeat for NRT-KUL
then splice it as a multi city on matrix, to price it out.
JFK-TYO
NRT-KUL
KUL-NRT
TYO-JFK
Then either bookwithmatrix
or reproduce the multi city on jal.com
key is to find X space on all legs, and I find that the method above is effective.
if you don’t know how to use matrix.....
advanced codes and put this
airline: JL+
Faring: F bc=x