Off the top of my head, I don't think there is an actual interface for other Users to do this. I would suggest the "Net User" command, but don't think that would work since FN is not running as a DC (in your environment). Only other thing I could think of is if they were able to SSH in (say via Putty) and change their password that way. But, I have not tried/verified this personally.
Guess in the end, if you really want this type of Control/Administration you are looking at needing some type of DC; whether that is with FN acting as the DC or there being another system as a DC.