I know this is a really old thread, but I've had the same question! Every time I take my puppy out (now 15wks old) I say "go potty". If he starts to go #2 I say "go poo"
I've done this every time, I swear! When I say "go potty" he will do whichever action he needs to do. If it's #2, I switch to "go poo", but I don't think he gets that one.
Yesterday I took him out and wanted to make sure he went #2. He hadn't gone in 12 hours or so, even though he'd had a meal in that time. He had plenty of opportunities, he went #1 outside twice in that twelve hour period, but no poo. I wanted to make sure he went because I was going out for about three or four hours.
I took him out, let him take his time, said both commands enough times to make me worry I was going to unteach them (he did go #1 though), then finally I gave up and went back in. I repeated this routine about 45 minutes later, still no poo.
So I guess he just didn't need to go? When I got back four hours later, I let him hang out with me for a bit, then I fed and watered him, then he took a little nap, then we went out and he finally went poo. It was really weird.
So I'm not sure if I just don't have it on command yet, or if he just thought I was crazy telling him to go poo when he didn't need to.
But I can certainly appreciate the need to have both on command... there have been times in his early housetraining days when he'd go #1 outside, then act like he was done, start playing with leaves, etc. Then once inside he'd start assuming the #2 position!