Well, it won't be easy, but you might be able to do it using the "Chart Areas" setting. I recommend you look at THIS SITE, specifically the "Creating a Correlated Bar Graph" section, and see if you can get some shading based on the values in the groups that will appear behind each grouping (e.g. by setting some max values slightly larger than the values of the group).

It will require some trial and error, and it might not be a box per se, but it could be good enough for your purposes. Good luck!

Cheers,

Eric