Slack matching is an optimization that determines the amount of buffering that must be added to each channel of a slack elastic asynchronous system in order to reduce its cycle time to a specified target. We present two methods of expressing the slack matching problem as a mixed integer linear programming problem. The first method is applicable to systems composed of either full-buffers or half-buffers but not both. The second method is applicable to systems composed of any combination of full-buffers and half-buffers.