Few pictures of using 2 servos. You need 2 bike spokes and carbon tubule, or outer part of bowden as guiding for spoke.

  elevator drive connection

  spoke to ailerons is braked and taken up to servo   

  spoke to elevator is altogether, guided through body , at one of spoke closure you can see ball for pull bar toggle

As oposed to aileron's pull bars, you have to bend elevator pull bars after puting it through body (at one closure of course). Groove for pull bars can be made by solder, stick with cyanacrylic glue.

    These pictures were place here, when I learn, that most pilots are making drives from bars with bowden only. It is necessary to utilize servo as best as possible and don't overload it with needless leverage ratio. In practice, deflections seems to be good at the ground, but in the air especialy during highspeed descending you pull up ..... and nothing. Air resistance don't allow move of elevons - you must adjust leverage ratio, not increase deflection. If you keep size of lever marked with arrow, servo works as designed.

Anyway, if some plane seems to be less sensitive on elevator, problem is not in servo or plane, but what you desire for servo. With HS-55 servos model must respond immediately in any behavior. 

   At last (but with bad grace) I crashed with sukhoi and here you can see aileron's design with one servo. This crashed plane (significantly overloaded - flight weight was 1100g) was repaired in 10 minutes.

  real deflection at elevator on Raptor

   delta mix at MiG-25 or other

  interesting design with lever of ship rudder. Both elevons of elevator are connected by 2mm spoke sticked on balsa, guided through body tail on LERX's surface (upper or bottom). Genial simple idea of mjr. EPP Věřtáta from Kladno commando.