To Chico,
Actually, the problem has already been (technically) solved. I have a capo which rolls. There is no makers name on it, but it consists of two hard rubber rollers; the top one which goes on the strings is wide at the outside and tapers into the middle to match the fretboard curve and the bottom roller is shorter and more tapered to fit on the back of the neck. The two metal rods the rollers are on (axles) are connected by two steel springs to maintain the tension. On one side the spring has a cap which comes off the axle so it can be attache or detached from the guitar. When not in use it can be rolled off over the nut. In use, it can be rolled from fret to fret in a tenth of a second.
Maybe your music store can track down one of these for you.