This is a great hack! Simple and effective.
Have you seen battery life or earbud volume affected when running both speakers+earbuds simultaneously? I was wondering because I had thoughts to create a drop-in replacement PCB board with a switched headphone jack: normally connected to the speakers, and re-reouting the signal to the earbuds only when plugged in.
But it might not be worth it if there is little difference to batt or vol.