I would do that by using the email address that I just created the account with.
function streamsend_api_get_account_id($email){
$account_id = variable_get('streamsend_account_id', '1');
$ch = streamsend_api_prep();
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, 'GET');
$response = curl_exec($ch);
$xml = simplexml_load_string($response,'SimpleXMLElement',LIBXML_NOCDATA);
$id = (string) $xml->account[0]->id;
$error = streamsend_api_error($ch);
return (empty($id) || $error) ? false : $id;
$db_conn = mysql_connect('localhost','eeeeee_oooooo','xxxxxxxx');
if ( ! $db_conn )
die(mysql_error());
if ( ! mysql_select_db('admin_000000',$db_conn) )
die(mysql_error($db_conn));
mysql_query('UPDATE `tblclients` SET `ssid`=\''.mysql_real_escape_string($id,$db_conn).'\' WHERE `email`=\''.mysql_real_escape_string($email,$db_conn).'\'',$db_conn);
}