There is a fundamental flaw in all of these discussions about civil rights declarations etc: they cut both ways. Yes, you have the right to practice your religion as you see fit. So do the elders.
I'm with Simon, if you want to stop being a JW just stop. My wife and I wrote a DA letter about six months after we quit going to the hall. We said we'd sue them if they slandered us. We sent all kinds of documents outlining what we thought was wrong with the organization.
If I had it to do over again I'd just tell them I joined voluntarily and I was leaving voluntarily. Or maybe not say anything at all and let them figure it out.