This minor modification worked for me: 
eval {
        no strict "refs";

        require "$fqn_file";

        local $SIG{'__DIE__'};
        ###$ref = $foo->can('f_preferred') ? \&{$foo . "::f_preferred"
+} : undef;
        $ref = $foo->can('f_preferred');
};

[download]
Read up on UNIVERSAL for more info.

Update: I too needed to read up on UNIVERSAL, as can does exactly what the OP was looking for without my redundant ternary operator.

---
It's all fine and dandy until someone has to look at the code.

In reply to Re: referring to packages indirectly by kwaping
in thread referring to packages indirectly by Brad.Walker

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