1) Slide seat all the way back
2) Remove the plastic covering the fuel door and trunk release switches by pulling/sliding them forwards. Be careful that you don't cut your hand when it finally gives. If you have to, use a screw driver with some cloth wrapped around it to pry a bit to loosen things up.
3) Remove the plastic bevel/trim pieces surrounding the fuel door release and trunk release levers. It's done by popping up the little plastic flip-up pin piece, and then sliding the forward half forwards and the back half backwards. A little bit of shifting around should get the sucker loose.
All the plastic in the area should be off by now. Now, hopefully you have small hands or long fingers. You should be able to reach under the carpet and feel a little round button/lock ring. Slide it into place so it surrounds the hole in your carpet. Take the hook that you have, and snap it on top of that ring (over the carpet) nice and tight.
Put everything back.