I don't agree that it's bad to do this- I've made many lagers, and even with 6 weeks at 34 degrees, the beer carbed up fine. There will still be plenty of yeast in suspension to carbonate your beer. I've done it many times, and so have others.
I probably wouldn't do it in this case, though. Here's why- cold beer holds co2 in solution better, and when you bottle a lager, you can look at a priming calcuator and actually reduce the priming sugar. Also, cold crashing is for clarity- in a stout, it seems like it would not matter. Lastly, temperature control. Most people who do this have a way to set a controller to keep the temperature stable. Sticking it outside might work- or, it might get unexpectedly cold and the beer could freeze and break the carboy. Or, the temp might drop so slowly that the beer temperature only drops a couple of degrees anyway.
I always look at risk vs benefits before I do anything.
What's the risk here? Well, a minute chance it won't carb up, the possibility that the carboy will break (again, pretty remote), the possibility of being a bit overcarbed for a stout (more likely), etc.
What's the benefit? A clearer stout?
Unless you have a ton of hazy stuff, I wouldn't bother.