I really like BennyK's idea. I would write 2 messages. I'd have one for the elders, and one for everybody else. I would probably deliver my messages through group texts. In the message for the elders, I would simply say, "I no longer wish to be recognized as one of Jehovah's Witnesses."
In the message for everyone else, I would explain exactly why I am leaving. I would include everything that Watchtower doesn't want them to know. I would even send them the ARC "presumptuous" clip of Geoffrey Jackson. Sending 2 different messages will take away the control that the elders feel they should have over
the situation. It will really mess with their inflated egos. When they announce you, everybody will know exactly why you are leaving.
The elders are bound to see your other message eventually, that's inevitable.
When they do, they'll probably wet their pants in shame. The C.O. won't be too happy about it either. It's the perfect plan.