The idea for a pot came from me.
A capacitor in series with a wire is a cap in series with a resistance - together they form a 1st order RC circuit, a very fast one. By adding a pot I can dial in the time-constant and effectively change the duration that it is effective. It's pretty much a blunt LPF - with that in mind you can see that I'm thinking about "HOW LONG the start up "problem" happens" (to quote lost_and_confused) ... and how to potentially deal with it.
The reason I'm not sure why your suggestion of a resistor will work is that this issue happens whatever state the arduino is in (or for that matter any other servo PWM source such a Pololu) - I mentioned this in post #4.
Also I'm not sure what you mean by 'stabilize the signal' - keen to learn though 