I know of people who have done this, but they are the ones who sell something big- house, vehicle, or something like that. You could also save money that you get/earn outside of your 'regular' income- tax return, child support, etc. Or of course, get a second job while not increasing your expenditures.
I save all money (in a separate account) that is not my work income- tax returns, current tax credits, bonus at work, any unplanned income. Out of sight, out of mind works well for me.