Juice Analytics gave up trying with Excel, but Robert said "Yes we can" et voilà !
The NY Times chart.
Robert's replica with Sparklines for XL heatMap function.
The file is available for download here.
Note : Robert added one line in the code to make the circles transparent, so the text behind could be seen.
Robert is also contribuiting to Chandoo's excellent blog Pointy Haired Dilbert.