John, in addition to Charlie’s basement tempo series all you need do, from the standpoint of general fitness and aerobic training, is monitor your heart rate during a regular tempo session- then match that heart rate via the performance of low impact exercises.
While this type of work does not have the same biodynamic transfer as the tempo runs themselves, it is very beneficial from a general work capacity standpoint and more specific to the muscles and how they function during the particular exercises.
In addition, with this type of exercise you may train a range of cardiac and aerobic abilities by making the necessary HR intensity adjustments relative to your anaerobic threshold.