I posted about this in my kegerator conversion
thread but I think it's a good idea so I thought I would give it a thread so it would show up in searches more easily.
I wanted a way to cool my tower that didn't require wiring up a fan since the fridge I used didn't have a lot of excess space.
My solution was to use a 1/2" ID copper pipe per beer line that extends into the fridge and up into the tower. The copper transfers the cool of the fridge along it's length keeping the lines cool. In all of my tests (and now in subsequent usage) the first pour of beer is the same temperature as any other. I also don't get that initial excess amount of foam that I've seen reported quite often.
I drilled a 1.25" hole through the insulation to snuggly take the 2 pieces of copper pipe. The pipe should extend into the fridge about an inch and go up the tower to within 2" of the goose neck on the shank.
Spray foam the void and make sure to lean the pipes back slightly away from the shanks so you have clearance. If you just bring them up the center of the tower you will have a weird kink in your lines. Here are the assembled shanks with 3/16" beer line routed through the pipes.
: Be sure to use a file to round out both ends of the copper pipe so that you don't cut into your beer line.