That’s a good question!
This is how I do it:
During the 1st day (MAP) we have determined a few interesting areas to work on: typically pain points or great opportunities to improve the experience.
On day 2 (SKETCH), I ask the participants to find ideas, especially in these areas but without being too restrictive. At the end of the Crazy 8’s I gather everyone around the Map and ask them to show to the rest of the team where their ideas would take place in the flow (without revealing anything more).
This ensures that the main parts of the experience are covered. If we realize that no one was inspired by a specific (important) step, we can still do one more round of C8 on this topic.
During the Solution Sketches, I ask the participants to fully develop their main idea, but if they are inspired by other parts of the experience, they can always use a bit of time to sketch some additional ones. Usually, these “little scraps” of new ideas will be useful to compliment someone’s else work.