Seeing as Hrok is the"smallest" in the company and fairly stealthy maybe he could attempt to scale the wall and remove the gatekeepers, making way for the main onslaught. If he had the aid of another such stealthy orc they could infiltrate and get the gates open while simultaneously watching each others backs.

Another option is he piggy backs one of his larger companions to help him shake the wall during shift change. Although even if some by night complications could arise.