Probably your best bet is to write a helper script called something like sendMail-cli.php something like this:

<?php
require_once 'sendMail.php';
extract(json_decode(file_get_contents('php://stdin')));
sendMail($fromName, $fromEmail, $to, $cc, $bcc, $subject, $messageHtml
+, $messageText);
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And then from Perl, you can pass data to that:

use JSON;

my %mail = (
  fromName    => 'Alice',
  fromEmail   => 'alice@example.com',
  to          => 'bob@example.net',
  cc          => 'carol@example.net',
  bcc         => 'dave@example.org',
  subject     => 'Test message',
  messageHtml => '<p>Test</p>',
  messageText => "Test\n",
);

open my $sm, '|php sendMail-cli.php' or die 'could not open pipe to se
+nd mail';
print {$sm} encode_json(\%mail);
close $sm;
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There are probably nicer ways to do it, but that's quick and easy.

Code is untested, but should give you a general idea.

(For bonus points, make sure that sendMail-cli.php cannot be called directly via your webserver, to avoid creating a spam gateway.)