I believe that their considering God and the "Society" as one and the same is literally hardwired into their brains in a manner analogous to riding a bicycle, typing or having an accent when learning another language. It only takes a few years of hearing the phrase "Jehovah's Organization" to get to the point where the mention of one word automatically lights up in the brain the other word making it a composite concept in the persons
You simply, in my opinion, cannot tease apart Jehovah and organization in their minds. You would probably have to be blunt and say "You're not Jehovah" or even blunter still, depending on the circumstances, "You're Organization never was, is not, nor ever shall be Jehovah's."