My Book into DVR Expander

Is it possible to turn a 250GB My Book Essential into a DVR Expander?

I would think all it would take is some sort of firmware change but does this even exist?

I don’t think so.  The way I understand it the dvr expander doesn’t really have firmware, because firmware prevents the drives from being controlled by the dvr’s.  You could always try it, but it probably won’t work without alot of dropped frames, if at all.