I did this copper pipe thing on my kegerator. I don't think it works very well at all. The copper pipes extend about a foot into my kegerator cabinet and are actually touching the cold plate that used to be the freezer comparment, but the tops of the copper pipes up in the tower are room temp.
If I were going to do it over, I would either install a fan to blow air up into the tower, or just do it with nothing and save myself the copper.
some pics to show the copper coming down into my cabinet as well as the loads of insulation I put on them up through the tower: