Riding pacelines safely takes practice and knowledge that the people in front of you are going to act predictably. Pick-up pacelines typically involve random club members who do not practice together or even discuss their technique, signaling, etc. These can be quite dangerous, especially if they are more than a few cyclists.

The best thing to do is to allow some extra space even if it means you don't get the optimum draft. If you have a group who rides together frequently, organize a paceline clinic and have an experienced rider explain the finer points of pacelines and practice together.