You must use the bone to make soup! If you want to, use some bits of meat in there too, make up a lovely minestrone or barley soup, awesome for winter!
For a barley soup, fry off carrot and celery, then add your lamb bits and bone, barley and cover with heaps of stock. Bring to the boil and simmer at a good pace for 90 mins. The bone will add extra calcium to your soup, and the barley gluten sort of thickens it up and makes it all hearty. Yum.

Would the vegans kill me if I said I miss cooking with animal bones?