dragShot script mod

Hey, so, I've got a script that allows one to drag and slingshot objects, as in angry birds. I didn't write it...it's by a very intelligent guy who wrote this post. It's a great script, but I need to be able to click anywhere on the screen and have the dragPlane in the script work on the object, appearing relative to where the user has clicked. Any idea how to modify the script? I DON'T WANT YOU TO WRITE MY CODE FOR ME, REALLY. I just want to know what to look for. I'm pretty sure it has to do with the raycasting, but I have no idea how this script works. I can pay you in honorable praises and titles!

Cheers.

S