...the only issue is that @pids doesn't seem to be globally referenced...

I'm not sure what you mean by that. This seems to work:

my ($fh, @pids) = pipeline(
  [qw(ls -1)],
  [qw(sed -e s/t/a/g)],
  [qw(sed -e s/z/b/g)],
  # Let's "hang" for 20 seconds
  [qw(sleep 20)],
);
eval {
  local $SIG{ALRM} = sub { die "alarm\n" };
  # Assume we're "hung" after 5 seconds
  alarm 5;
  while (<$fh>) {
    print "$.:$_";
  }
};
if ($@) {
    die unless $@ eq "alarm\n";
    # Kill the sleep process
    kill 1, $pids[0];
    # timed out
} else {
  close $fh;
}

print "Pids: @pids\n";
[download]

Sorry if I'm misunderstanding, but glad you got it working.