i'm not sure about how to get to the rear deck...I remember someone had a post about that somewhere on the forum....but for the grills, to my knowledge you can't use them because the stock grills are riveted onto the rear deck (the grills and cover come off as one)...I would know because I broke a couple of the rivets trying to pry that off.
I guess you could do a custom install with the grills if you really wanted to.
here's that link btw:
http://invision.aleromod.com/index.php?showtopic=438