Pony/horse, pretty much the same difference when it comes to training something like that. It couldn't hurt to ask for his help and I wouldn't be much help either. When we used to break mule teams, we would start with a 4 horse evener an put the green team on the outside and a good broke team in the middle. That way even if the young one freaked out, the stout broke one beside him would keep him in control. Then we would just transition them to going by themselves when they had some handle.
Sorry I can't be more help. I would love some pix of Snapple pulling a cart. LOL
She is beautiful.