Preheat the grill on High (approx. 400°F). Place each potato on a small square of foil, brush with olive oil, sprinkle with a little coarse salt, and wrap.
Bake on the warming rack for one hour. (Reduce heat to med/high after you remove the potatoes). When the potatoes have just 15 minutes remaining, slice the butter into pats and place in a large mixing bowl, with the bacon bits, and sour cream.
Unwrap the potatoes and slice in half lengthwise. Use a tablespoon to gently scoop out most of the potato, leaving a nice potato-skin boat. Place the skins upright on a perforated baking sheet or veggie rack.
Mash the potatoes with the butter and sour cream. Add one cup of the cheese, plus milk, salt, and pepper to taste and mix together. (Do not whip)
Use a large spoon to heap the mashed potato mixture into the boats. Top with the remaining grated cheese and garnish with fresh chives. Place the baking sheet on the grill for 20 to 30 minutes and then remove, garnish wtih remaining cheese, and serve.