Light the grill. Place all the coal on one side of the grill.
Make a deep insertion into the roast. In a bowl, combine apple, prunes, sage, apple vinegar and butter. Mix well. Rub the pork with some salt both on the inside and outside. Cut a criss-cross pattern into the rind. Now, try to get as much of the stuffing as possible into the pork. Tie it all up using a cotton string.
Sear the roast for about 15 minutes, turning every now and then to make it brown all around. Place the roast as far away from the heat as possible. Add the birch shavings and the apple wood to the coals. Put on the lid on the grill. Since temperatures will vary according to your grill the best thing is to use a meat thermometer. The roast is done when the internal temperature has reached 160F (70C).