It is so hacky I can't help myself from posting it. What if you created a waterfall chart that had your little red boxes and then just placed a line chart over it?
Where I was going with the R visuals was that you should have absolute control over the visualizations to be able to code what you want without going down the custom visual route. ggplot2 should provide the control over the chart to place those boxes on there if you can find the right R code.