Hey Jason,
Instead of this:
$post_data = array( 'method' => 'limelm.pkey.generate', 'version_id' => $version_id, 'num_keys' => 1, 'num_acts' => $quantity, 'email' => $email, 'api_key' => $api_key, 'nojsoncallback' => 1, 'format' => 'json');
Use this:
$post_data = array( 'method' => 'limelm.pkey.generate', 'version_id' => $version_id, 'num_keys' => 1, 'num_acts' => $quantity, 'email' => $email, 'api_key' => $api_key, 'nojsoncallback' => 1, 'format' => 'json', 'for_tfs' => 'true');
Notice the "'for_tfs' => 'true'" line.