I like this idea, yet not just with a singular letter, but many, so as to raise suspicion of a uprising of "underground" JWs within the congregation. I think I can get more than a few from my congregation to send a copy of this letter. The elders (well some will agree with Wingman) won't know who is all involved just that is a consensus of many in the congregation.
If you are an angry EX-JW, then consider this multi-posted letter as away to drive the local elders to a paranoid frenzy of Underground uprising. They will not know whom to accuse. All you have to do is make 10 copies mailing them from your town.
Those who want to see the tower fall in shame, again join in the letter campaign. Perceived United they stand, Witchhunt Divided they will fall.