You can create a new Swift_Mailer
instance and use that:
// Backup your default mailer
$backup = Mail::getSwiftMailer();
// Setup your gmail mailer
$transport = Swift_SmtpTransport::newInstance('smtp.gmail.com', 465, 'ssl');
$transport->setUsername('your_gmail_username');
$transport->setPassword('your_gmail_password');
// Any other mailer configuration stuff needed...
$gmail = new Swift_Mailer($transport);
// Set the mailer as gmail
Mail::setSwiftMailer($gmail);
// Send your message
Mail::send();
// Restore your original mailer
Mail::setSwiftMailer($backup);