I have had a really tiny 4cm piece of cutting (not like the ones you buy, it was much thinner!) in a drawer for two or three months. When I found it, I discovered it had been growing in the meantime. It had grown like 2 cm, totally white and thin, because it had absolutely no light and water. I planted it this spring, and it started growing, it became a healthy green and I have high hopes for it to become a strong plant!
I have cut another plant this fall, it was 50cm and I cut it down to a few centimeters. It hasn't received any water since, and almost no direct sunlight (winter in Europe...) and recently it started growing two new sprouts.
San Pedro are the toughest mofos you can imagine. I think if you put a cutting in the fridge for a month, it will still be growing inside the fridge. Some people say they even produce more mescaline under stress, so putting a cutting in the fridge for a few weeks will even make it stronger!
From what I've seen, I think a San Pedro cutting of decent size can live without soil and light for at least a year.