i tried blowing cold air into the beer tower, and it will not work properly without a significant amount of insulation.
my beer tower was not thick enough to accommodate enough insulation to really matter unfortunately.
with fridges and freezers, keep in mind you are working with EXCEPTIONALLY low capacity systems.
in your average fridge, just running an old style 100w light bulb inside will completely negate the cooling capacity of the fridge.
the only reasonable way to cool the faucets IMHO, is with an on demand type system, meaning a system that only attempts to chill the faucets when you engage a switch or sensor of some sort.
your fridge will in all likelihood not be able to keep the faucets cool 247 while maintaining the desired temp inside the freezer.
ive seen folks try work a solution by placing reservoirs of glycol water directly in contact with the evaporator... thereby chilling below the air temps. this chilled water is then periodically pumped up to the insulated tower and circulated around the shank of the faucet. This setup should work well enough as long as the volume of tubing is small with respect to the volume of the chilled reservoir, and you do not try and chill the faucets 247.
also its worth noting that you could build some sort of cover for the faucets that would reduce the heat exchange... something like an outdoor hose bib cover would well, though look awful.
id suggest buying something with the highest BTUH per cubic foot possible...
