As an Elder, you have access. To information, to documents.
Document yourself with everything you possibly can. Anything that helps prove discriminating policies, suspicious transactions, coverups policies, changes in beliefs, etc. Elders have access to information not available to common rank-and-file. Use that access. It may prove very valuable at a later stage.
If possible, tactfully, incentive people in your congregation to be open-minded about information sources. Encourage people to be receptive to sources outside the Watchtower publications (don't ever mention WHY). But this opens a backdoor in people's minds. If they will use it or not, who knows, But it's there.
Cast doubts about the Slave's ability to correctly interpret Scriptures, by pointing out many doctrine changes in the past - but always putting a positive spin on it, like, how they are humble and willing to admit that they were wrong, or how they are always trying to let the scriptures guide them. At some point, people will start asking themselves why an organization supposedly led by God himself has to change doctrine so many times. Couldn't God get it right the first time around?
Then, when you can no longer help people anymore without attracting negative attention, resign from Elder. Don't give much explanations, say that you're burned out, depressed, whatever. They will try to squeeze you for more information (such as determining if you're a covert apostate, or if you have committed some sin secretly), but don't crack under pressure.
When you feel ready, fade out. Or disassociate. For your sanity's sake. Living a life you don't believe in anymore is truly damaging for your mental health.