Not directly applicable to the OP, but I have had luck showing up early enough to catch an earlier flight to my international gateway. I've just gone to the ticket counter and said "I got here early and I'd rather wait in ATL/MSP/DTW/etc. Can you put me on the earlier flight?" The 2 or 3 times I've done this the flights were wide open so seats were not an issue.

The "23 hour connection" on an international itinerary is a much under appreciated "trick."