Easy Tomato is a modified version of TomatoUSB, which is in turn a modified version of Jonathan Zarate’s excellent open source Tomato firmware. Relief Labs has worked to make this powerful firmware accessible to less technical users through easy to use documentation and a simplified interface
I'm not sure if this feature is already implemented, but I could not find any reference to it in the documentation.
TomatoUSB comes with a tool to spin down usb disks when not in use: http://tomatousb.org/tut:spin-down-usb-disks-when-not-used
However this tool does not seem to be included in EasyTomato. Is it as easy as finding the binary and uploading it? Can it be included by default?