Originally Posted by
Airsicknessbag
They could enter the US at their point of departure a la Bahamas or Canada.
None of those islands have pre-clearance.
Originally Posted by
Airsicknessbag
Alternatively, the flight could arrive at an international concourse at HNL, and if you prove the immigration officer your travel started at GUM (by passport and boarding pass) you can enter the US without immigration formalities.
You'd still be going through the process, just without showing a passport. And I doubt it would work this easily since there is too much room for faking it.