You've gotta remove the back seats as well as the back side panels. Then remove the rear tray, you should be able to get the tray out by sliding it towards you. There's a few tabs that latch on underneath that you'll have to reattach later.

I've copied a few pages from the service manual that show the diagrams.
http://individual.utoronto.ca/krobertson/interior.pdf

You can get the full manual from www.hondahookup.com/manuals