Can anyone tell me what the likelyhood of this is?
Very unlikely at the moment.
If you are sucessful in completing the CPL/IR and Tfly offer you a job it will be on the same basis as everyone else as far as I know - you will fill in a basing preference form and you will get the base you want that has a vacancy. There is no fixed time at a base, you can move as quickly as you like as long as there is a vacancy for you to fill.