bivalving a cast

CPT 29700-29715 are listed under Removal or Repair in the Application of Casts and Strapping, and the code states "Removal or bivalving". It also says "Codes for cast removals should be employed only for casts applied by another physician". If a cast is applied and then is bivalved, how do we bill for the extra work involved in bivalving the cast if those codes are only to be used for casts applied by another physician?