That is really clever. It's amazing how such a simple thing can make you so happy.
One valve that I found a few years back is McMaster 6790T42
http://www.mcmaster.com/#catalog/120/481/=qkrfx0
Under Brass push button valves. With a normally closed action, you'll never have to remember to close the valve again. I think this would still work well with your mounting method.