You could do

my $iter = get_value_iter($oWkBook);
while ($iter->(my $item_ref)) {
   $$item_ref =~ s/^\s+\n$//;
}
[download]

sub get_value_iter {
   our $val; local *val = \$_[0];

   if (ref($val) eq 'SCALAR') {
      my $ref = $val;
      return sub {
         my $sub_iter = get_value_iter($$ref);
         return $sub_iter->($_[0]);
      };
   }

   if (ref($val) eq 'ARRAY') {
      my $ref = $val;
      my $key = 0;
      my $sub_iter;
      return sub {
         for (;;) {
            return 1 if $sub_iter && $sub_iter->($_[0]);
            return if $key >= @$ref;
            $sub_iter = get_value_iter($ref->[$key++]);
         }
      };
   }

   if (ref($val) eq 'HASH') {
      my $ref = $val;
      my @keys = keys %$ref;
      my $sub_iter;
      return sub {
         for (;;) {
            return 1 if $sub_iter && $sub_iter->($_[0]);
            return if not @keys;
            $sub_iter = get_value_iter($ref->{shift @keys});
         }
      };
   }

   {
      my $ref = \$val;
      my $done = 0;
      return sub {
         return if $done;
         $_[0] = $ref;
         $done = 1;
         return 1;
      };
   }
}
[download]

Scalar::Util's reftype can be used instead of ref if you wish to traverse objects.