I'm not aware of a loop feature, but when faced with this challenge, I've gone into the XML itself and copied the row blocks over and over.
<format type="color" field="Duration">
<colorPalette type="minMidMax" minColor="#FFFFFF" maxColor="#6A5C9E"></colorPalette>
Then it's just a matter of find/replace.
You may want to consider grouping data into panels. Having 51 distinct panels may exceed the number of concurrent searches and perform slowly. Or have a drop-down to select the site. Yet another option is to have each one set up as a scheduled report, and then use those reports in the single big dashboard.