I don't want to rain on the parade but I believe letters to HQ will be shredded by a low in the food chain drone never to be seen by the paedophile protecting GB.
To me the way to fight is indeed as stated to hurt them in the pocket book.
The most effective way is to raise awareness of the disgusting cult manipulation. To tarnish the name of watchtower(R) beyond repair. It's all about gettting information out publically.
Not hearsay. Not personal opinion but by exposing the true nature of the cult to the nations. This will slow their growth even more as people avoid the JW cult like the plague it is.
Raise awareness in whatever legal and appropriate way possible.