Buy a job lot of 737 from different airlines and companies and mod them up?
We could have a Mk 1, Mk 2 and a Mk 4 all in one go. Some could be in full MPA rig, some could be part MPA/Pax and some could be Freight. After all the Mk 1 Nimrod was originally an MPA/AT, 46 pax wasn't it?