Just dump your updflash.bin at the root a fat32 (msdos) formatted usb stick and do the following….this should work with any version of xell/xellous::
For best results of getting the usb device detected. Remove the power plug from the console
after running the MS dashboard. Then reinsert the power plug, insert usb device and then
boot into XeLLous.
More on this whole Xell process stuff here from xbox scene