Yeah, I've done something similar with Cage, but I've only had maybe a couple of hours with the demo so I haven't been able to experiment much. I used Sub Zero at fist and couldn't pull anything off (combos) with him. Johnny and Scorpion have some standard moves that knock opponents into the air for juggles... sub zero doesn't really have this and I'm guessing it's because he is given freeze moves instead. The only way I know to start a good juggle with Sub-Zero is to freeze... get in close, jump straight up and hit "square" (back punch I think?)... then you can pull off a few hits, freeze, followed by a few more hits and maybe an x-ray.
I don't think we'll see too many crazy sub-zero combos until the final game releases and we get the tag team matches unlocked. You pair up sub-zero's freeze attacks with somebody like Johnny cage that has natural juggling moves.... watch out!!!!!!