Good question. On models with the traditional shifter there is a red release handle under the cupholder on the center console (remove the cupholder inserts and then grab the cupholder and pull up firmly, it will disengage from its clips and pop off), I have seen where it is on my 2013 but I have never operated it, knock on wood.... You either push or pull the red lever to manually engage neutral. If you have a newer model with the dial-type shifter, there should be a similar pull handle in the same area, with some sort of safety lock next to it (turn the lock to "unlock" position and pull the red nylon handle to engage neutral.) Make sure you have your foot firmly planted on the brake pedal if you are parked on an incline! The manual handbrake release is down there as well if you engaged it. Neither emergency procedures are detailed in the Owner's Handbook, unfortunately.
Before you do that though, have you tried jump starting the battery? Even with a dead alternator you should be able to get enough juice from a donor vehicle - or a portable jump starter - to start the engine and at least flip the shifter to neutral before you disconnect the leads of the jump start cable from the battery posts.