Another more gimmicky/novelty option would be stick shifters-which were popular on 70s era Stingray, Krate, Spyder type bikes in the early 70s. They usually mount on the top tube, some mounted on the head tube, some on the stem. Some existed in 1x5, 1x6, 2x5, 2x6, and 2x7 versions. Maybe the 2x7 were indexed but the other were friction style.