Yes it's possible. I don't have the creation kit under hand, but you want to copy a MGEF (for exemple the fire rune magic effect) and instead of a fire damage add the unrelenting force effect. I don't remember if the last one is a script effect, but this is the start.
you could also look here http://www.creationkit.com/Magic_Effect for other hints.
after you created the magic effect you use it creating a new SPEL. you want, maybe, to copy the fire rune one to see how it works. Sorry but now i can't be more detailed. But well, it's a start
