For comfort I've modified the script "Precompose and trim to layer length.jsx" to place it as a dockable palette. I found this script really useful and thanks to all developers.
hope this updated script might save you even more time.
Can download from the link below
file name: Precompose and trim to layer length Dockable.jsxhttps://drive.google.com/open?id=0ByXUcJJ4U9Utd2NvREFncGJTeW8