I'm not sure what the normal way to welcome Noobs to class is, but I've always felt that "jumping them in" was a good policy. I mean, who wants to go to a martial arts class and flail around like a spazzy noob and come away feeling "Well, that wasn't too bad, those guys didn't really smash me...". I mean, if that's the case why bother taking a martial art? Just lift weights and be a strong spazzy noob. It's even more important of the noob IS Strong and spazzy. If they come and you let them just smash away at you and they leave feeling like they won then they might not come back.
If instead of feeling like they won, or even feeling like they held their own, they get completely dominated for five minutes by someone they outweigh by 50lbs then obviously what they are there to learn WORKS and is worth while. Towards the end of class, or on their second class you can let them work on stuff, give them pointers, etc... But that first class should be a clear demonstration that they are completely helpless against a trained opponent.
So the next time you get a first day noob in the class do him a favor, jump him in.