There is no other way ,as far as i am aware, to use any Chip(usb) that does not have a unique serial number (so thats virtually all clones) than to use UDEV and the USB port number - which means you have to plug the devices in the same port each time. If you Google it you can a number of tutorials on how to pick up the port number with Udev. OR just buy a real FDTI chipped device which have unique id's.
Most of the above 2 chip sets also suffer from the same problem as the Prolific - lack of unique characteristics. Ok if you just replace one of your Prolific chipped adapters with another with a different chip then you will be ok.