Presuming you're talking about midi, then this feature is indeed already on our Mac end, and has been for years.
If this isn't automatically turned on when you start up, here's how to activate it on Mac:
Go to the GS menu under Options menu, and select the bottom option, "Set Panning to Stereo" (see screenshot). You should then get a notice of confirmation that informs you of the split.
From there on, this should stay active until you deliberately go back in that menu to change it, i.e. even if you select an entirely different song project or mess around with the mixer, this should still be active.