Assuming that there are people who already know who JW's are and already don't want them bothering them, I wouldn't go into the JW beliefs aspect too much on the flyer. It may make the householder want to ask questions the next time a JW calls rather than put them off.
I think it might be good to give them a brief explanation of the "Do Not Call" option along with a pre-printed do not call form letter that could be easily sent off to HQ or the local Hall. Or if one wants to be truly devious, one could send a Do Not Call request in for every house in the neighborhood and bypass the householder altogether. If we all did this, what do you think would happen? You'd have to make sure the letters were all different looking. Heck....you could just open the phone book and start writing down names and addresses.
Of course you know that in a year or two there'll be and assembly experience about how a study was started as a direct result of someone having received one of these letters and being interested enough to ask for a study.