Calculate the wing loading for this model. Then ask yourself if adding two more servos for flaps is within the realm of reality. Might not be. Does the wing have seperate aileron servos now? If so, flaperons as Futaba calls them would be the way to go. You can then set up the ABK function which is basically down ailerons and up elevator. You can set it on a switch or the throttle stick. How much elevator deflection are you using, and is the model nose heavy at all? What kind of Tx do you have? Seems like with the functions you mention, it has some potential.
I use the E->F function on lots of models. This is an old U control trick from yesteryear. It really smooths out loops and flares by giving the wing a slightly different shape and a bit more lift. Let me know_Bob