Today Ikari released the first version of 'freeBOOT' for xenon (v1) and falcon (v3) consoles with JTAG/SMC-Hack. This hasn't been tested yet, so try/use at own risk for now.
To quote: A 'rebooter', allows to 'reboot' the 360 into an MS kernel after starting it with the JTAG Hack... in this case (freeBOOT v0.01) it should reboot the console into MS...