Include Session variable on message body

Hi,

Can I include a SESSION variable just on the message body of the sent message?

If I put the tag [session] on the message body and include the following code on functions.php, would it work?

function include_session($cf7) {

	session_start();
	$cf7->posted_data["session"] = $_SESSION['variable'];

}
add_action( 'wpcf7_before_send_mail', 'include_session' );

Is there a better way (a better hook) for doing this?

Thanks in advance,
Jo?o.