Just because several people have mentioned it: you aren't stuck with an older kernel if you want to do this.
1) Start with an exploitable old kernel, dump your CPU key from Linux and take a backup of your NAND with an Infectus.
2) Go on Live and upgrade to the latest kernel.
3) Back up the NAND again with the Infectus so you have a copy of both kernels.
You can now use the flash tool to change the region of the *new* kernel, and flash that back on. You now have a new kernel with any region you like

Also, you now have the ability to downgrade as well, if you want to boot Linux again, or if something else interesting to do with the exploit is released: the flash tool can patch the old kernel dump so that it will work even though your eFuses have been blown.
Hope that's clear enough for everyone

Edit: Oh, also, you can use certain xD/SM card readers instead of an Infectus, if that's easier to get hold of. See xboxhacker forums for how to do it
