Bake the potatoes in the oven until just done. Cut the potatoes in half, scoop out the potatoes and, in a bowl, whip them with the milk, chipotles, garlic, and just enough additional milk to hold them together. Place the potatoes back in the skins.
Place the potatoes on the grill, away from the direct flame, and place on the grill. When the lamb chops are done, the potatoes should be hot.