It is sobering to review the circumstances of the RAAF mishap with B707 A20-103 at East Sale in Victoria some years ago. An extreme set of circumstances involving aspects of inappropriate operation .. with essentially predictable results. Well worth a read for multiengine instructor pilots who fancy that their flying skills are up there with the aces.
One needs to keep in mind that book Vmca is quite specific, the real world figure rather variable according to configuration and ambients. While there may be a case for exposing a pilot in training to general aspects of Vmca, I suggest a better option is to stay away from it and let the TPs come up with the numbers for the AFM.
If you MUST play with Vmca, do it with consideration, sufficient height to provide for recovery if it gets away from you .. and be prepared to close the other throttle to get rid of the yawing moment.