Seriously...I mean if we happened to know someone who is having a Bible study, know a Witness who is having serious doubts, ect., we could print out some really good information and (anonymously) put it in their mailboxes!! Or something like that.
If we know someone who is studying, we can send them a very nice letter. It is hard for people to put down a letter that is directed to them personally. Also, by mailing it, it gets into their mailbox the legal way. Merely placing something at their door might appear indifferent and impersonal.
I use to let people know at the church I attended for a short time, that I was an ex-JW. They would ask me what to do when someone they knew was studying. I would visit with them and discuss many details and help them to reason with the person they felt concern. This way, the JW Bible study received even more caring help and discussion than a letter from me.
Even still, people do what people do. I had one women call me because she was studying. She wanted to know what ex-JWs had to say. So, I loaned her Crisis of Conscience and In Search of Christian Freedom by Ray Franz. She read both, and we spent many hours on the phone discussing her concerns. Eventually, she decided to continue studying and became a JW. Well, at least she had moe information going into it then most JWs do. Hopefully someday she will wake up and realize what she did to herself.