How to preserve pep power?

Solution 1:

Yes, you can switch your party around. This quest is very luck dependent in the early game. Later, you can get a couple of members "fired up" and switch them out. Once you're ready with 3 characters close, switch them all in and they will pep up together.

Solution 2:

FoxMcCloud is right that it's a lot easier to do when you can switch people out. What I found to help is trying to make the party members "use up" their pep as soon as possible -- by using pep powers if they have them -- so that when the next character get's their pep, it is more likely to lineup with the other characters. Early on (when you only have 4 or fewer characters) "fired up" seems to happen sooner, so this works fairly well. Also, keep in mind that many pep powers that require 3 people do not require them to all be pepped up.