If you don't need interaction, consider a two-stage fork, which is safer than having one program both send and recieve with IPC::Open3, since you can never deadlock by being the wrong state. For example:

if (open RESULTS, "-|") {
  # I am the original process, so read from <RESULTS> below
} else {
   # I am the kid
  if (open STDIN, "|-") {
    # I am still the kid, but my STDIN is now piped from the grandkid
    exec "your", "big", "application";
    die "can't find big application: $!";
  } else { # I am the grandkid: be a data pump
    print "$_\n" for @input_data;
    exit 0;
  }
}
while (<RESULTS>) {
  ....
}
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This double-fork data-pump is a nice pattern to keep in mind.