I decided to try a different approach. Using PHP, you can make a small app that will accept a chunk of text, parse it, and allow you to copy it. Basically a web app that you can submit the text to and it will add the tabs.
This would just need to be hosted on a web server with PHP enabled, then it will work on both Mac and Windows. If you don't have a web server, you can install a local copy of WampServer or XAMPP on a machine somewhere and give it a try. (XAMPP has an installer for Mac.)
<html>
<head>
<title>84th character tab inserter</title>
</head>
<body>
<?php
if ($_POST['text'] != "")
{
$text = $_POST['text'];
$i = 0;
$output_text = "";
for (; $i < strlen($text); $i+=84)
{
$output_text .= substr($text, $i, 84) . "\t";
}
$output_text .= substr($text, $i);
echo '<pre>';
echo $output_text;
echo '</pre>';
}
else
{
?>
<form method="POST" action="">
<textarea name="text" cols="100" rows="10" onclick="javascript:this.value = '';">Paste input text here...</textarea>
<br />
<input type="submit" value="Parse" />
</form>
<?php
}
?>
</body>
</html>