Before going crossfire, power and disable question

I've got one 4890 card already and considering a 2nd one to crossfire.

I want to know if it's possible to "Disable" the hardware in Windows management console or Device Manager without rebooting the computer. If so, does disabling the 2nd card mean that it won't consume as much power anymore?

My reasoning, if I'm not gaming, I don't need both cards running and I don't need the power draw / heat production.

Thanks in advance.