Buy everyone, I have to go now.
Thanks to those who had useful suggestions (namely Robert), they helped me to modify my approach:
When JWs come, I'll take the tract, write on it www.freedomofmind.com, and hand it back with a greeting of a nice day.
I'm not very fond of grandiose gestures (ripping the tract), anyway. And this approach will accomplish what I wanted:
1 - they can't count it as a placement
2 - they can't give it to anybody else
3- It will show them what I think about it
4 - it will make me happy