From the article:

If you don’t want to be identified, you can disable mssfix, just set it to zero on both server and client.

As for the OS/browser fingerprinting, I suppose you could just use p0f to figure out what your VPN "exit node" is running, then modify your user-agent to match.

Interestingly enough, it assumes that if it can't figure out either OS or fingerprint, they match:

    Detected OS   = ???
    HTTP software = ???

    ...
    Fingerprint and OS match.