It seems to me, that if you can shut off the charcoal, by shutting all the vents, you can control the heat by using the vents. (At least, that's the way I see it.)
My ProQ will shut down the charcoal at the end of a cook, so I'm pretty sure that I can bring down the temps by adjusting the vents. (I'll try tomorrow, after I finish my turkeys.)
steve