Link to the guide
xXhighpowerXx managed to do it and put together a tutorial on youtube, big thanks to him!
Link to his post
Also there is this detailed blog post of derPeter, I recommend reading it to everyone interested in this hardware hack. Link to the post
This requires disassembling the fireTV, soldering electronic parts and also basic linux skills (and a linux machine)!
Try at your own risk!
Also he updated the information in the GTVHacker wiki linked above, so everything you need to know is there.
MAKE SURE TO ALSO READ THIS POST, AS THERE IS A SOLID RISK OF BRICKING YOUR DEVICE IF YOU ARE NOT CAREFUL! Thanks to ingrimsch for talking to the gtv guys on IRC and providing the log.