Neat. So the servo is directly-mounted to the camera carrier (ie, no linkage/sprockets). Good idea.
Harley Michaelis developed an internal control surface linkage system, the RDS (Rotary Driver System). The RDS has a splined collar that fits over the servo output shaft that would be perfect to connect the servo and camera carrier. More at http://www.proptwisters.org/rds2/
FWIW, if you don't wan to use a servo arm.