I have decided I can't be arsed with our crystal-maze ticketing system. In order to go with my friend we each - seperately - need to be booking tickets. Making sure that no one gets in.
Neither of us are allowed to book tickets that leave a single ticket for you know, you other person, outstanding.
One of you adds the other as a "friend" on your account. Add two tickets to your order, then allocate one of them to your friend.