I'm looking at flying US-LON-XX R/T this summer (where a number of XXs yield cheaper fares than flying US-LON), and will need to check a bag, but on the return would prefer not to check my bag on my positioning flight to XX and on the return flight from XX to LON (depending on the length of the layover, I would leave it at the airport or at the hotel), but would then need to check it for the flight from LON-US. Possible?