I was introduced to the concept of partial capoing many years ago by the great acoustic guitarist Harvey Reid and by Jeff Hickey, who developed the Third Hand capo (an elastic capo designed exclusively for partial capoing). These guys both were users of Shubb capos for regular capoing, but were WAY into the possibilities of partial capoing. In addition to using a Third Hand, I noticed that Harvey had modified one of his Shubb capos by cutting it down so that it skipped the outside string and covered only the next three. He got some really wonderful sounds with this partial capo. Shortly thereafter I saw Chris Proctor using one he had customized, evidently inspired by Harvey.