The way it works now at every run the nginx cookbook will overwrite the nginx config file and after that the nginx_ssl_proxy will write that file again. This is quite inefficient and makes backups harder.
You can overwrite templates like this: http://2.bp.blogspot.com/-1NQTb3vxQnA/UJ6SrYEafHI/AAAAAAAAEy4/_dZjl8rEWtM/s1600/library_app.png
I hope this helps!