This was discussed at the meeting, I can't recall if you were in on the conversation though. I know Jake and Thomas were though.
Personally, I would abandon the copper pipe because unless you're running refrigerant (ie:freon) through it, I doubt it'd be very effective. I'd also do away with the 4" pvc - run the beer lines through 2" pvc and seal both ends, put a fitting at each end and essentially build a 2" pvc version of a wort chiller ...pump cold water in the top and out the bottom. I'm pretty certain it would work and only cost a few bucks to build