That's exactly what I started doing about 10 years ago. I'd paid off a vehicle and had grown accustomed to making a roughly $400 per month vehicle payment, something I'd been doing with fair regularity for a number of years, so just kept putting that same amount, since I had already "budgeted" for it, into a special savings account that I named my "Car Account". Later I poked it into a money-market account with a brokerage house in order to make more interest. Since that time I've bought two new and one used vehicle by paying cash, haven't made a car-payment to a creditor in a decade, but I keep making that payment to myself!! Feels good, plus the money is there if a guy ever needed it for some real emergency. I become increasingly convinced that with the economy as uncertain as it seems to be at present, the only legitimate form of indebtedness, certainly in any sort of long-term sense, is one's home mortgage.....and even that can be shakey as we have seen lately, at least under some circumstances and/or in certain parts of the country.
You sir are a smart man. Thats exactly how it should be done....if you can.