Paul,
Yes you could do it that way but you also could edit while you record to DVD. If you are watching the program while recording to DVD just hit the pause button (on the DVD recorder) when you don't want to record that part of what you are playing back from your 721.
By the way, I have switched to just using RW DVDs (mine uses DVD +RW). The price has REALLY dropped in the last few months (under 60 cents per DVD when purchased in bulk). They can be erased and re-used about 1000 times. It is surprising how many things I have put on DVD +R and now I wonder why I did that. A program that may be a "keeper" now might not be something that you think is a "keeper" in a year (or even a month). Using ALL RW disks solves that problem.