The "Jazz Styles" are probably too jazzy for what you're looking for. If you get the "Pop Styles" (free with the OSX program, but you'll need to buy them for the iOS app) there's a "Shuffle" and a "12/8" setting. On specific songs (like Jimmy Reed stuff, for example) you might need to edit the bass here and there to stay on the root ( /E ) but if you're looking for a bouncy straight-8 beat (like "Big Boss Man") you're pretty much out of luck. Maybe if enough people request more blues styles, there's always the chance they'll be added to future updates.