This will prevent scouts from going to whatever Action Center they feel like. This will also limit the number of scouts participating at each action center and hopefully the lines as well. The activities will be open to anyone in their region on a first come-first served basis. Scouts may participate by patrol or individually. If Scouts don't linger and move swiftly they can accomplish a lot.
Planning is a key.
There should not be an expectation that a Scout can do everything at a Jambo. It's like going to Disneyland. Troop leaders can, however, observe their Scouts and cheer them on. Adults assigned to troops often show encouragement, take pictures, videos, and hold gear. Make sure the scouts have their water.