[pHaestus]

They have several kinds of ball valves with 1/2" fittings at Home Depot that would work. The most promising are copper with a center larger than the barbs (to allow the ball) and then a lever on the top bolted on. The lever that they come with are large, but there is no reason you couldn't just unbolt it and replace it with a much smaller lever or knob of your choosing. They were I think $7 or so. There were also some white PVC ones with round knobs. It looked like the other types of vavles really restrict flow while the ball valves don't look like they will affect flow at all.