looking at File::Find::Rule, it looks like you can use the exec() method for arbitrary user-defined rules. Something along the lines of:

my @results = File::Find::Rule->file()
                              ->exec( sub { length($_[1]) < 255 } )
                              ->in( $dir );
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I would use Data::Dumper; die Dumper \@_; in the sub to verify what's getting passed in; also look at the pod for the exec method.