Error with Win32::OLE->new('Excel.Application') and a filename with unicode chars

Question

I would like to open an excel file on Cygwin that have a ü in the filename but I get an exception:

OLE exception from "microsoft Office Excel":

Here's the program I am using:

use 5.014;
use warnings;
use strict;
use Win32::OLE qw(CP_UTF8);
use Win32::OLE::Const 'Microsoft Excel';
use Win32::OLE::Enum;

$Win32::OLE::Warn = 2;
$Win32::OLE::CP = CP_UTF8;

my $excel = Win32::OLE->new('Excel.Application', sub {$_[0]->Quit;});   

my $filename = "/cygpath/c/fooü.xls";
$filename = `cygpath -wa '$filename'` or say "Damned";

my $book = $excel->Workbooks->Open({ FileName => $filename, ReadOnly => 1}) or return;

What can I do to properly encode the filename? I already tried encode('utf8', $filename) as well as cp1252 and latin1.