The sensible thing to do would be to retain the STN base for 40-odd aircraft, then fly W patterns into LTN during the day. That would retain the early morning/late evening slots at STN, hit BAA, and utilise the only sensible alternative airport at times when it has capacity. (Luton's problem is parking overnight).
It would have best effect on the services with several rotations from STN during the day, like HHN, CIA, PIK, DUB, etc
It would offer London-bound pax a choice of airports and save FR a shed-load of cash. It also keeps FR tapped-in to the all-important and lucrative London market.