Lets think of what you would be trying to accomplish with this. You would be taking a compact fridge with minimal cooling power designed for a very compact well insulated space and then doubling or trippling that space you want to cool while insulating it the best you can and keeping much larger items (kegs of beer) that will probably be going into it warm and cool them down to serving temps...asking all this from a system built to keep a couple cans of pop, a gallon of milk and a pack a hot dogs cold with a package of bacon in the freezer. Im not trying to sound like a smartass but thats how I would break it down if a friend asked me the same question. I think thats asking a lot to turn it into a kegerator for a couple corney kegs.
Edit...I agree with above in tbat the materials involved you could maybe look at something better suited. Again, what is your budget for the build?