I would imagine it works similar to when there is FP. There should be a CM at the start of the queue, and you can ask them for a rider switch pass. Then the people in your party that are riding first (group A) wait in line, while the rest of you (group B) find something else to do. After group A rides and exits, you switch off, and group B gets to bypass the line. Even if FP isn't running, there should still be a CM directing you where to go. You would probably still enter through the FP line.