Spray grill rack with non-stick spray and prepare a medium direct heat grill.
Cut the potatoes into 2" quarters. Use a metal skewer to pierce each potato piece and place in a bowl with the garlic, 2 Tablespoons of the olive oil, and the lemon zest. Toss to coat.
Strip rosemary brances of all of the leaves except for 1" from the small end, saving the leaves. Using a knife, cut the fat end of the branches into a point. Thread the potato wedges onto the rosemary in a red, white and blue sequence, filling each branch equally.
Grill the skewers for 25-30 minutes, turning several times, until golden and crisp.
Meanwhile, in a small bowl, whisk together the remaining oil, vinegar, mustard, horseradish, chives and rosemary leaves.
Place potatoes on a platter and drizzle with the olive oil mixture.
Serve with grilled sausages. Serves 6.
* If rosemary branches are not available, use wooden or metal skewers but still use fresh chopped rosemary in the sauce.