[hobbit] multiple RRD graphs for a single column

How can I get Hobbit to display multiple physical RRD graphs for a single column of data? Specifically, I'd like to have two distinct graphs (each with their own Y-scale) for a single data column that is being generated from an external script. This would be similar to how Hobbit sometimes shows multiple graphs under the "disk" column. I can't seem to find this anywhere in the documentation.