For phat consoles on dashboard version 15572+, you simply write one of TX's "new" ECC images to your console's NAND (they are named for each board) and use a standard CoolRunner (wired up for RGH2) to boot into XeLL and get the CPU key.
Once you have the CPU key, you treat the console as a regular RGH2 install.
J-Runner was updated recently to include these new ECC files.