I had to go LIS-EZE last year so of course I routed LIS-LHR-HKG-JFK-EZE. All in transit, though leaving the airport at both HKG and JFK. Didn't measure the mileage at the time but it is 20,320 per great circle mapper (also didn't think it was particularly exceptional as a trip; flying east but having CX F service/beds made it very easy, and the JFK-EZE flight is not bad as there is little time change). However it was a waste of a ticket, but I didn't have time for side trips.