What I've learned from pull pull systems:

1) Unless you keep the cables perfectly parallel, it's gets complicated. That means the servo horn and the servo arm have to have the cables connect at the exact same distance from the rotation point (servo shaft and control surface hinge). If the cables cross, there will be slack in one of them at full defections unless you make some changes to the setup (too much detail to go into here).

2) They should not touch the fuse where they exit. This can make for some huge slots.

I would think that the simplist way to do a split elevator is to mount the servos in the tail on the side of the fuse so the cables are on the outside but it might be kind of ugly.