i did it with a 1.7 dagger i bought of the ah and just melee attacking him with elemental force on. didnt seam to hard
He definitely doesn't need frost damage to freeze him. I tested it ealier today using only fire and shadow and he still froze.
I was worried at first, but for two resets I've been easily able to shatter him with double felguard and double tentacle trinkets(Yogg10/C'thun trinkets). I've gotten lucky so far and got a pet from him each reset. =D