
Well, I'd say a) don't do that.
B) project backups don't take up that much space. I do them all the time, and if it's a really important project, I'll manually export them twice a day.
The only time I ever, ever delete backup projects is once the project is delivered. Then and only then, I'll delete all but the last couple of backups. I'm on a feature now where I have 6 backups, one for each day I've been working, and I expect to be done tomorrow or the next day. So maybe I'll delete the backups after Friday or so.
Drive space is cheap. I'm not worried about filling up a large drive with DRPs, which are typically well under 1GB or so.