The olive oil is already on the bow, so it would be worth a shot if he is not satisfied with his finish, and shellac will stick to about any thing including your fingers. Shellac base with poly over top is compatible, and wax over that makes a good finish. He could also use a mixture of turpentine, linseed oil,and Bee's wax, and apply ,and heat into the bow. Olive oil ,or no olive oil it will suck into the wood. Apply to the wood untill the wood stops sucking it in. Then Bee's wax, and wipe down.