[edit XanTium: more info about this hack: http://forums.xbox-scene.com/index.php?showtopic=696317
what you need:
your 8955 live console + cpu key
a 2nd unbanned console
nandpro b + flash cable
use nandpro and dump nand from unbanned console.
flash xell and use jtag hack to obtain cpu key.
use flashtool to extract file system.
dump nand from 8955 console.
use flashtool to patch nand dump with kv.bin from unbanned console.
save patched file (patched_kv.bin).
open degraded + 1888 fs.
create 1888 downgrader image (downgrader.bin) from your patched_kv.bin file.
flash downgrader.bin to 8955 console.
attach hdd + ethernet cable and boot console.
connect to live and update to 8955 dashboard.
console is now fully working and unbanned!