If you go to the Cunard website you will see the QM2 is doing this trip on July 8 and July 22. She docks in Southampton which is the opposite end of the country to Scotland. You could fly from Southampton to Scotland and then get a flight back from Edinburgh or Glasgow to NYC.
Southampton to edinburgh or glasgow.
www.flybe.com flys both routes.
southampton airport is 15 minutes by taxi from the port, fare approx £16.00.
note well. luggage allowance on flight is 20 kilos, anything over is charged extra.