I may be misinterpreting, but I think what you may be looking for is a Marimekko chart. Rob Austin has put an example together here - Marimekko in Tableau
A bit tricky and you'll have to flip the rows/columns shelves, but I'm hoping this is the direction you were looking for.
Jimmy, yes, a Marimekko chart is what I am after but quite tricky to construct (was hoping there might be an easier way)! Thanks.
Daniel, thanks for your suggestion too.