The only way to stop a master from transmitting is to close the channel. When you do this, you will lose synchronization, and your slaves need to search again to reacquire. Searching drains a lot of power (relatively). If you are currently only putting the ANT chip to sleep and not losing synch, it might be a worse power drain to have to search.
One more advanced option is that you can change channel period on the fly, so when you don't need your master, you can reduce the channel period to the lowest possible setting (0.5 Hz) then bring it back up when you need it again. To do this you would need to send messages letting both sides know when the switching was taking place.