So you'll never have a permanent unchanging v6 address to ID your traffic with.

Privacy extensions are orthogonal here; they only affect the suffix, not the prefix. As for dealing with a changing prefix... I'm afraid you'll just have to find some way to automate the DNS updates. You can do it with a program running on one of the servers -- I can't suggest a specific one offhand since I have a static prefix and haven't needed it, but they do exist.