Or you could cheat and tell the software your device does not have power commands. So when you enter the activity, the device stays off. You add a delay in the startup sequence and then you add the power on command for the device.

Then you add the power off command for the device for when you leave the activity.

(sorry for resurrecting a very old discussion, maybe there are more advanced techniques nowadays, but I found this while searching for a solution for myself and I thought about sharing)