I actually did this a couple of years ago, and had it working pretty well. Unfortunately I lost the cogs and stuff for it, otherwise I'd just give them to you.
But you just need to have a pulse that fires the projectile at the player from the hook or vise versa. Using something with trailthing and a short timer is most effective. I actually just used the laser trip mine laser template straight out of hideki's enhance pack at the time.
I found it was easier it fire TO the player FROM the projectile when the hook was moving, and FROM the player TO the projectile when the hook was attached. That just had the best visual results.
I wish I could remember the code right off hand...just check the JKspecs for the verbs to find a vector between two things. I think it was VectorSub(). Good luck.