If you look around enough in the menus, you can figure out how to do this, but I'll make it really easy for you. There are 3 different keys that can have custom functions assigned to them for use in PASM modes. Custom controls don't work in the Intelligent auto mode (iA).
You can set these up from the Custom Keys option in the Setup menu.
The 5N has two soft keys along the right side of the screen the bottom one is user programmable. The right button on the rear 4-way controller is unlabeled and it is also a user programmable button. There is also a Custom function that uses the center button of the main dial to bring up an on-screen menu that can be set to show up to 5 user-selectable functions.
My current mapping is:
Bottom Soft key next to the screen: Brings up main control dial for shooting mode selection
Right side of Direction pad: HDR menu
Custom center button: Brings up ISO, AF/MF, Creative modes, RAW/JPG selection, Flash settings.