Used poj's knowhow to make it work. (what was I thinking yesterday evening, AlignH is for indentation, not merged cells). Code is smaller to boot!

use Spreadsheet::ParseExcel::Simple;

my $xls = Spreadsheet::ParseExcel::Simple->read('excel.xls');
foreach my $sheet ($xls->sheets) {

  #unmerge
  unmerge($sheet->{sheet});
  

  while ($sheet->has_data) {  
    my @data = $sheet->next_row;
    print join("\t", @data),"\n";
  }
}


sub unmerge{
    my($oWkS) =@_;
    print "--------- SHEETNAME:", $oWkS->{Name}, "\n";

    my $range = $oWkS->get_merged_areas();
    for (@$range){
        print "
        start row : $_->[0]
        start col : $_->[1]
        end row   : $_->[2]
        end col   : $_->[3] \n\n";
        
        $oWkC = $oWkS->{Cells}[$_->[0]][$_->[1]];

        for my $iR ($_->[0] .. $_->[2]){
            for my $iC ($_->[1] .. $_->[3]){
                next if ($iR eq $_->[0] &&  $iC eq $_->[1]);
                print "SET [$iR][$iC] <= [$_->[0]][$_->[1]]\n";
                $oWkS->{Cells}[$iR][$iC]->{_Value} = $oWkC->Value;
            }
        }
    }
    print "--------- DONE Unmerging.\n";
}
[download]

Output:

--------- SHEETNAME:Sheet1

                start row : 0
                start col : 0
                end row   : 2
                end col   : 0 

SET [1][0] <= [0][0]
SET [2][0] <= [0][0]
--------- DONE Unmerging.
cat     Fluffy
cat     Vera
cat     Manxie
[download]

Caveat: The {_Value} is still not guaranteed to be in the topleft cell from a range (as misterperl had it in the second column), so the code might need to be expanded to first SEARCH for a defined {_Value} in the range. Then have that as the source data cell, then iterate over the range writing all other cells that are undefined...

You can access the functions from within Simple like:

$sheet->{sheet}->get_merged_areas();