al posto di mettere come link il file excel metti un file php:

scarica il file

e in scarica.php metti:

codice:
$filename = $_GET['filename'];
$filedimension = filesize($filename);
header("Content-type: Application/octet-stream");
header("Content-Disposition: attachment; filename=$filename");
header("Content-Description: Download file");
header("Content-Length: $filedimension");
readfile($filename);