What about this:

build_url( 

      account => $account,
      fname   => $fname, 
      lname   => $lname],
);
sub build_url {
   my (%args) = @_;
   my $account = $args{account} || '';
   my $fname   = $args{fname}   || '';
   my $lname   = $args{lname}   || '';
   my $other   = $args{other}   ||'';

   ...
}
[download]

There, it should prevent it to be out of order right?