Well...I opted to buy a CO2 Pipe Freeze kit and it worked like a charm. We purged the hot water lines w/ cold water so the temperature was about 60*F.
In about 35 minutes we had plugs developed.
One thing I'll say, which was previously said, have plenty of spare CO2 on-hand.
We did 6 freeze plugs on a 2" CU line and consumed almost 100 #'s of CO2. This included about 1 hour of cutting & fitting time after the freeze.
Based on this experience, I would recommend this method over the Ridgid Machine.