Different servos have different responses to a lack of control pulses.
What are you actually wanting to do? A servo might be the wrong answer.
ANALOG FEEDBACK SERVO
All you need to do to make one of those servos is open it up and solder a wire to the center pin of the pot. That is a regular ser in the video, it was just modded with an extra wire. If you don't give the servo a signal, you can easily move it. Believe me, I use them for RC planes.
Actually, if you aren't giving it a signal, rotating it by hand will NOT damage it. I do it a lot and all my servos still work.