Motion layer...sort of

Hi everyone…
I m wondering if someone can tell me if there is a way to make like motion guided layer for tool like pencile and then make it like mask layer…

Basically what i m trying to do is that i want to make a huge letter but in a movie clip so the final resault would be pencile moving and writting…

If there is an action script i woul love to use it.

Thnx for all the help.