Column Chart with Three-layered horizontal access - Any ideas?

Hi Guys,

My buddy asked me for some yelp creating a chart with a horizontal axis that has three layers, and I'm not sure if it is even possible. Two layers is relatively straightforward and he may have to live with that, considering a google search won't turn up anything about three layers. Can you guys offer any suggestions?

I've attached an example file with my attempts. Basically, I'd like the third and most detailed axis layer to be the legend, reproduced six times over.

Thanks in advance for any help!

Best,

Scott