Hi Ben,
You can try building one bar chart and one line chart separetely , both with same height and width.
Then align one of them by 0 from the top of the other, and 0 by the left.
Set the background of one of them to transparent .
Finally , bring the transparent background to forward ( order )
Regards,
Rogerio
Take a look atUsing an Interactive InfoGraphic in your WEBI Report
For a better explanation