Are you lookin to add the MDI to the OEM location in the arm rest, or are you looking to put it in the glove box?
I did a thread that describes how to get to and install the RNS-510, so this should give you the info you need to get to the back of the RNS.
If you are going to install the MDI in the center console arm rest, you need a center console that either housed a CD changer or an iPod dock. Otherwise, you have to buy a new center console with support for the cd changer and a new air conditioning rear vent.
I'm going to look at the glove box version of this. Looks to be MUCH easier.
You can get this from the parts department: 5N0 057 342