Ian, that is why myself and others play left hand bass[songs like Whiter shade of pale]..

My primary keyboard has bass inversion[slash/bass]..but for intricate bass lines as well as walking bass we prefer playing the bass line and comp with the right hand..
In this respect the Casio WK3000 works fine..
BTW, if I recall Casio had a module[tabletop] in 1985-86, based on the CT8000..[it may have been an CT800]..