Don't bother with splitters and reversers, you'll never get things perfect, even with digital servos. The proper way to do this, is with a radio that has an extra channel and dual elevator programming. I'm not sure about JR but with Futaba the 7C is the cheapest with these features. If you really don't want to buy a new radio, then mount a single elevator servo in the fuselage and use wheel collars to Y a second pushrod onto the the first one, so you'll have two pushrods, one for each elevator half. Use a servo with twice the required torque rating.
Or else live with a plane that rolls while looping...