We've had problems with monopolies in the past but only because people didn't want to let go and give someone else a chance, we're all pretty capable up-front and that helps. Perhaps you might see if there's a way to arrange it so that people who aren't-fronting can sit near-front and observe what's going on so that they can get the idea of how to cope with being outside. Then perhaps a slow transition could be made to where they had some control over how things were done before they had to be outside alone and responsible for what happens.

As far as you learning to let go of the front goes all of that might help as well, giving you confidence that they can all handle themselves. It'd also be good if the person who was out knows that they can always fall-back and give you the lead if they are uncomfortable, that way you can take a break yet still be confident that if anything that's difficult to handle happens you won't have to be left-out of the loop.

Also its just good to think of falling back as taking a break, a vacation so-to-speak. Other than that its just something I've found you have to learn to be "ok" with