what you after is a lot easier than gradient (I should know after writing it myself, well 90% anyway). If you want some help with writing it into a script just add me to wlm and I'll give you a hand. I recomend you have a look
here for understanding how to do commands and
here for saving this into the registry.
I didn't really want to do it for you because it is a nice simple-ish script to start with and it always feels good when you write a script.