Have done it by using the rotisserie gadget. Have seen it done beautifully that way but ours turned out very greasy. I'm not sure a pork joint would cook through well enough if placed on top, and I wouldn't try it if it had a bone in the joint.
Another way is to wrap the joint in foil and place it deep in the embers. A clay flowerpot is often used with this method too. Prevents the meat burning on the outside. That's how I'd do it.
Let us know how it turns out.
PS: Get another clay flowerpot and pop some bread dough in there and you'll get a nice fresh loaf to go with it!