I've never done it, but I too have a side by side in my garage. Right now I keep the beer in the freezer side. The problem I see is how to control the temps in each side individually. I think both the fridge and freezer use a single compressor. I'm acutally just getting ready to go out and drill an exploratory hole in the fridge.
Draft 3: Belgian Dubbel
Primary 1: German Hefe