A\\kern-.2emB (or whatever value you'd like)

Thanks, but what I want is for this to happen automatically every time the pair occurs, without having to repeat the \kern command.

You have to edit the font metrics file in that case.

I wouldn't recommand changing the font metrics because it would make your tex code less portable. You can define a simple command like:

\def\fz{\symbol{383}\kern-0.14emz}

I suggest using \f instead because command names are restricted to basic ASCII. Using \symbol{383} also makes the command usable in different encodings or language.

Hope this help