In my opinion, the no strict 'refs' solution is the obvious and easy one, and so far the only arguments I have seen against it have been from superstition.

Just for arguments sake :-)

In this module we do not want any arbritary subroutine executed. We just want the "format token" subroutines executable.

At the moment this is not made explicit - it's implicit in the fact that FETCH can only execute single letter functions, and all the format token functions are single letter functions.

We could document this in POD or a comment, but my personal coding philosophy is to, as much as possible, have the code document itself.

As soon as we do:

my %lookup = (  
    a => \&a,
    D => \&d,
    X => \&X,
    x => \&x,
    d => \&d,
    ...
);
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we make the subroutines we want to execute explicit in the code. This is a good thing - and hopefully not just superstition :-)

While I would immediately refactor the subs into the hash as anonymous subroutines I think that that first step is a useful one - and not just monkey code.