For HS-55's (and similar micro servos) take a piece of medium fuel tubing and cut its length the same as the servo width, then slit one side so it'll fit over the servos mounting ear. Use a t-pin to put a hole in the tubing and force a mounting screw through it. The tubing should keep the screw in place while you position the servo over your pre-drilled holes and screw the servo in place.

Hogflyer