Not to belabor the point, but is your hard drive so full that you can't just record them? It seems to me that you are dramatically missing the point of having a DVR, or of the DVRs capabilities. It would be like waking up at 5:00 a.m. every day to set the alarm to go off at 6:00.
You can set the 625 so that it only has the latest episode in the hard drive. My wife and I like to watch the NBC news. It is set to record every day, and dump yesterday's episode. That way, we only have the one latest episode of the news at any one time. It is a "set it and forget it" type deal.
The purpose of live buffers is not to act as a second hard drive, the point of live buffers is to stop what you are doing to get a snack or go to the bathroom (or swat flies, as we were invaded yesterday

). Something else to consider, the live buffers live somewhere, and that somewhere is on the hard drive of the machine. Add 2 hours of HD live buffer, and you necessarily reduce the number of hours that the machine can record on the hard drive, and AFAIK, the live buffers take up more space than recorded programs, it is not 1:1.