that is an interesting idea, I would like to see someone try that.
I have seen SATA to eSATA cables could always make a eSATA kind of port on the xbox allowing for external hard drives and docking stations.
the only thing that might hold this idea back is the format of the drives and the external enclosures connector boards may not all work together, but would be cool to see done.
lol, i liked and hated jtagging, took my 6 hours to jtag my first xbox, but it was worth it, loved customizing my dashboard.
but i think as long as you are using only 1 drive and the drive is formated properly to be used in the xbox and there is no controller causing issues on the external drive end then it should work in theory, but who knows.