I don't know if this helps but here's what I'm thinking...
On electrics you thread the pull pull cable through the outermost hole in the servo arm, across the top of the arm and back down through the opposite hole. You adjust your elevators (the kevlar can slide across the top of the arm) then C/A the cable in place on the arm.
For giant scale you could do the same thing on a large bellcrank, utilizing 2 "EZ keepers" to lock the cabes in position once adjusted. Since the cables run through the same holes, there's no assymetry (assuming that the belcrank is centrally mounted).
Another way would be to use 4 wheels, one on each elevator half and two bolted together on the servo. In both systems you've got 2 loops of cable that terminate in ball links at the surface.
Another way is 4 cables, 8 ball links bolted to the bellcrank and surface. Whether bolted top and bottom of the bell crank or one on top of the other, you will have some differntial in throw due to different geometry's.
I use a bellcrank on large planes because I've had servo's get "rachety" on pull pull and find that the case tops have worn throwing the gears out of alignment. 2 servo's on a big Cap had the center gear pin walk out of the top.
Central Hobbies sells a nifty belcrank that you mount in the tail, just in case you get tired of visuallizing cats cradles with fishing line.
Chris