At our races here in South Africa, we actually pee wherever we want to. Just pull up on the side of the road, turn your back to the other runners, and there you go. Nobody gives you a second look. In the first few k's of the race, it's not unusual to see a row of guys lining up next to each facing a wall for a few seconds
You'll even see some of the ladies go down on a bended knee and just shift a part of their shorts with one of their hands