I wanted to implement some FTF stats, but regretfully it is rather difficult. I can't in a straightforward way check it via Okapi without parsing all log entries. I'm trying to find a way to do it in a reasonable way, but didn't figure it out yet.
FWIW, Project-GC checks for word "FTF" in the log to figure it out. I don't think many people put it in their logs (I know I don't usually) so it is not the best approach.