I am no longer maintaining this fork, as the changes have just been too much, and I've changed tactics for OTP to something much simplier, and more importantly doesn't need to be updated unless XIVLauncher's mechanism for receiving OTP tokens from the XLAuthenticator changes. I'll post a link once it is available.
I've now been able to finish and test my tool for filling OTP tokens in XIVLauncher. You can find it here. I've provided both a Windows and Linux binary, but it should be easy enough to compile from source with a simple clone and cargo build.