It's automated. Ever wonder what that little "beep" does when you scan your boarding pass enroute to the plane?

That's how they know you flew, knew if you didn't get on the plane and they need to pull your bags, or know if you get in the wrong plane.

Your only option is to scan, get on the plane, then hope the gate agent isn't watching and sneak out... but that could risk some sort of major incident you don't want to be responsible for.