1. A patient-specific surgical guide for intra-operatively creating a patient-specific augment adapted for mounting a prosthetic implant on a bone of a patient, the patient-specific surgical guide comprising: a base fixture including a mounting surface having a bone retaining portion thereon within which an unformed augment blank is receivable; and an interchangeable patient-specific cutting guide removably engaged to the base fixture, the patient-specific cutting guide including a semi-spherical shaped shell having one or more guide slots formed therein, the guide slots defining cutting guide surfaces which are customized in position and orientation for said patient and configured to guide a surgical implement to re-shape the unformed augment blank to create said patient-specific augment, wherein the patient-specific augment has a size and shape corresponding to a portion of the bone adapted to receive the prosthetic implant such that the patient-specific augment will conform to said portion of the bone for abutment therewith; wherein the patient-specific cutting guide is mounted to the base fixture for displacement between an open inoperable position and a closed bone cutting position, the bone retaining portion of the base fixture being accessible to receive the unformed augment blank therein when the patient-specific cutting guide is disposed in the open inoperable position, and the cutting guide surfaces of the patient-specific cutting guide being disposed in position to allow said re-shaping of the unformed augment blank when the patient-specific cutting guide is disposed in said closed bone cutting position.