Using File::Basename isn't that easy indeed, cause you got to suggest him the operating system of the client.
You can do it by checking CGI server variables but i prefer the regex way, it's more straight forward IMHO.
Maybe split solution could be more readable, even if less efficient:

my $new_file_name = pop @{[split /\/|\\/, $full_path_name]};
[download]

$|=$_='1g2i1u1l2i4e2n0k',map{print"\7",chop;select$,,$,,$,,$_/7}m{..}g