homemade premix dispenser / freezing beer

I've been inspired by a premix soda dispenser that chicompany sells:



I would love nothing more than to buy this, but at $400+ shipped, its difficult to justify buying something this much with no guarantee that it might not work in a month.

With that said, has anyone ever constructed something similar? IE a small 1 cubic foot freezer with copper beer lines inside of a tub of water that freezes when you turn it on? I figure as long as you do the math, and figure out how much copper tubing / fins you need in the block of ice, that you could make something very similar for pretty cheap (used 1 cu ft freezers can be found easily for $40).

My question: how would something like this, as well as the premix soda dispenser, keep the beer in the lines from freezing? Would you just need to make sure that you set the temperature of the freezer to something like 30 degrees? It would take a while to freeze it initially, but I think that's how the premix unit works also.

Would that keep it from freezing the beer inside the block of ice? Any thoughts?

Sorry, for those that aren't familiar, the idea is that the block of ice cools the liquid to about 34 degrees, and you can keep your kegs warm wherever you want them (in a cabinet, etc).