Would like to see this as a standard for dumbbell chart type. Allowing for 3 values in the data array.

Showing Low and High by default and setting the 3rd value as Mean, Median or Mode

This also then being reflected in the data table.

Hey. I had a similar need : I wanted to display the average curve of a serie, and the series itself, on the same chart.
This is what I did : http://jsfiddle.net/6gXfu/ I used "groupPixelWidth" and have a pretty nice result. You can change groupPixelWidth and the zoom to see how it does.
I hope this has been of some help !

(I even use it in a live chart -> updating from a server every 'n' seconds; and it works fine)