The Genisis Flyer is a Single speed frame with no derailer hanger, and track ends, so a cassette hub is really a no go, have you looked at Shimano Afline, although the rear dropoups may stop this, Afline comes in 8 or 11 speed, you may find it cheaper to sell the Genisis and get a bike with Afline bulit up, something like the On-One Pompetamine