I totally agree. I am Right Handed/Left Eyed.
I learned when I was about 8 years old to shoot rifles. I started with a right handed .22.
I shoot rifles, shotguns, anything long barreled with my Left Shoulder and Left Eye
I shoot All handguns with my Right Hand and Left eye.
He WILL get used to it. When I started, it was no issue whatsoever. It felt natural from the get go. Hope this helps.