Get JL to restart KIX-SIN-KUL?

As far as Oneworld goes, only MH and 3K operate on that route and neither will credit to AA at this time. Have to wait until MH joins the alliance at the end of the year and 3K only credits to QF and only on the most expensive fares.

You could try the QF codes, though I'm not sure if they would credit to AA or if they'd even let you book under the QF code without a connecting flight into SIN. But really, not much point spending the time looking for a creditable flight for all of 20 mins in the air.