I don't see what is so bad about standing outside peacefully with a poster. The good thing about doing it at the memorial is that there will be so many inactive JWs, "worldly" family trying to make an effort, and bible studies there too. The memorial is very guilt inducing for inactive JWs. As an inactive person I felt guilty, that I was basically squandering Christs' sacrifice by not living up to my dedication. Maybe if I had seen a poster at the memorial I would have gotten out sooner. When you have doubts, concerns, and questions it helps to know that others have them too, and where to go for help. Alot of JWs may not think to research on the internet out of the blue, may be too afraid.
In terms of whether it is appropriate to demonstrate on their most holy of nights, they should be able to handle that. This is the same religion where folks would wear giant placards, play phonographs at doors, knock on doors on other people's "holy days" Christmas, Thanksgiving, Hannukah, etc. without any regard for their feelings. Let's also not forget about street witnessing, bus stop witnessing, workplace witnessing, incidental witnessing, telephone witnessing, witnessing through the mail, cemetary witnessing (totally despicable), business territory, and I'm sure I've left something out. Shamefully I must admit that I've done most of those things. The point I'm trying to make is these are people who are pretty cool with using shall we say, unorthodox methods to get their message out.
We all participated to some degree in using unorthodox methods to "teach people the good news" when we thought we were doing the right thing. What's wrong with using the same methods to help get our brothers out?