Peter says: Pooping on the potty — possible or impossible to train?

I’m going to keep this short, sweet and, admittedly, a little stinky: How do you get your kids to poop on the potty?
 
I’m proud to report that Addy has been doing an awesome job peeing on the potty. (Not the toilet…her little potty.) She hasn’t wet a diaper in about a week and has been wearing Pull-Ups. (Next week we graduate to panties full-time.) But every time she has to poo, she insists on us putting a regular diaper on her (not even a Pull-Up) and she creeps into a corner to do her business. Lisa’s terrified of her getting constipated, so we haven’t been pushing her. But time is running out, and we want to keep encouraging her.
 
So, now that peeing is better than it was a week ago, I want to know: Is it possible to train kids to do Number Two on the toilet? How do you/did you get your kids to poop on the potty?