Here's a possibility that would require a redeye and an overnight in FLL and use a nested roundtrip. Fly from Seattle to PHL (2372 miles), connect to somewhere based on fare for another 500 miles. Nest a roundtrip to FLL in there out of that city for another 500+992 miles each way through PHL. Stay on the beach in FLL one night and reverse direction. Total miles come out to 8728. A grind, but doable over a weekend with the bonus of a night on the beach.