In the last day I've been working on this very problem and had downloaded the same spreadsheet as you to try to figure it out. I've attached what I've put together, with two funnel plots - one for the PCT ratings data in the spreadsheet and the other using the Superstore Sales data.
For the sales data, I created calculated fields to find the overall average profit ratio, along with standard error and intervals. Just plotting this in Tableau leads to reference lines straight across the entire view. I added two more fields, one for a Bin Size and second to calculate what bin the sales would fall into, then converted that Sales Bin into a discrete (blue) measure and put it on the Columns shelf. That creates panes, which are then used for the standard error reference lines so they end up with a funnel effect.
For the PCT data, I first generated a field in the Data worksheet that identified the appropriate n value in the Bounds worksheet. Then I copied & pasted both data sets into Tableau. In Tableau I created the bins as above, and laid out the data on a worksheet.
There are a couple issues with this setup: Tableau doesn't plot marks where there isn't any data, so there are no bins for some areas and the funnels look jagged. In addition, each bin creates a new X-axis in each pane and with some modication of the axes I can come close, but they're definitely not continuous.
Any other ideas on how to do this would be most welcome!
funnel_plot.twbx 1.2 MB