I want to use the Bible to help him realize that there's no such thing as a "representative of Jehovah" here on earth.
Perhaps you can get him to reflect on the inconsistency of the claims being made by the F&DS.
On the one hand they claim that they are not inspired but are being 'led' by the holy spirit and that they are imperfect and make mistakes.
On the other hand anybody who sincerely disagrees with them on a matter of substance will be accused of apostasy and DFd.
One minute submission to their teachings is a matter of life and death and the next they throw away teachings they have held for many years.
Would it be reasonable to think that if god was using a 'channel' to spread truth on the earth that they would be guilty of major errors?
'As for you, the anointing you received from him remains in you, and you do not need anyone to teach you. But as his anointing teaches you about all things and as that anointing is real, not counterfeit—just as it has taught you, remain in him.' - 1 John 2:27