Step 1: Remove the package of giblets (if any) from the body cavities of the hens and set aside for another use. Remove and discard the fat just inside the neck and body cavities. Rinse the game hens, inside and out, under cold running water and then drain and blot dry, inside and out, with paper towels. Loosen the skin from the meat of the game hens.

Step 2: Make the herb paste: Place the herbs, garlic, salt, and pepper in a food processor and process to finely chop. Add the mustard followed by the lemon juice and 1/2 cup of the oil to make a nice thick paste.

Step 3: Holding the hens upright (place in a bowl or pot if necessary), spoon about 1/8 of the herb paste into the space between the skin and the body of each hen, massaging the skin to spread the paste evenly over the hen. Insert 2 sage leaves under the skin of each hen, trying to position a leaf in the center of each side of the breast. Place 1 teaspoon herb paste into the cavity of each hen.

Step 4: Truss the game hens. Arrange them in a nonreactive roasting pan or baking dish and spoon the remaining herb paste over them. Let the hens marinate in the refrigerator, covered, for as little as 30 minutes (while you preheat the grill) or as long as 2 hours.

Step 5: Set up the grill for rotisserie grilling and preheat to high. When ready to cook, skewer the game hens on the spit, remembering to attach one set of grill prongs on the spit beforehand. Attach the spit and turn on the motor. Grill the hens until golden brown on the outside and cooked through, 40 minutes to 1 hour. Brush the hens with the reserved oil as they roast. To test for doneness, insert an instant-read meat thermometer into the thickest part of a thigh but not so that it touches the bone. The internal temperature should be at least 165 degrees.

Step 6: Transfer the hens to plates or a platter and let rest for 5 minutes. Remove the trussing strings and serve at once.