Cancelation Fee

Is it possible to set up a Cancelation Fee?
Ideally, i would like to be able to set up a cancelation fee for subscriptions that are being cancelled before certain period of time.
For example, we are selling software subscription with monthly payments, but require that you need to subscribe to it for at least 6 months. Ideally, we would like to set up a cancelation fee equal to amount of money they had to pay for the rest of 6 months period.
But if ideal set up does not work, is it possible to have any cancelation fees?