Thats interesting that a new vehicle doesn't have an aux port available.
On my '99 Pontiac, there is a "hack" for adding your own aux port. Here's the link.
I don't know how helpful it will be to you, but it might revolve around the same principle and work the same way if you can identify the wiring and are confident enough to splice into it or bring to a trustworthy place to do the work for you.
Granted, this is not for an Infiniti, but the logic might still work.
http://ls1tech.com/forums/stereo-electr ... apter.html