I've already been doing this. I first send the postcards (in envelopes) to friends in other states and they mail them for me so the postmark isn't from where I live. If I get caught someday and the elder gives me a talkin' to I already have my response, "So, as a JW you are objecting to unsolicited religious material showing up at people's homes?"
I think it would be great if friends/family could "subscribe" to a service where you pay a fee and postcards are regularly sent out to the address you provide. This way the shunned ones might be able to make some headway with loved ones without it being traced back.