the AUX input is strictly audio and will not transmit data in any way to the screen.
even the cable connected from the iPod to the AUX is Audio only.
the only i can think of this to be done is to use the dock connector of the iPod to draw the info, but then you would need to integrate the info into the screen which means reprogramming the Nissan screen software (in other words not worth the effort)
for changing songs from the stock controls, the easiest way i can think of would be to buy the iPod remote that can already control the iPod device, then take it to an electronics shop to replicate the IR/RF stream for each command.
you would then need to build your own IR/RF transmitter and connect it to the stock controls. this way the original usage of the controls would not be affected once you disconnect the iPod and return to radio/cd audio.
** PS: i'm supposing a remote for controlling the iPod exists.. i dunno, does it?