I don't see a way with just Archive::Tar but how about combining it with File::Find:

#!/usr/local/bin/perl -w

use Archive::Tar;
use File::Find;

$arc = Archive::Tar->new();
find( \&archiveit, "/whatever/dir" );
$arc->write( "my.tar.gz", 9 );

sub archiveit {
        $arc->add_files( $File::Find::name );
}
[download]

-derby