Um if this is for a research project, some sort of installation piece, or hobby project it is probably doable but if this is for some sort of product that you intend to sell it is very likely a bad idea. This is because it is very likely only going to be achievable through substantial hardware modification of your Kinect sensor.

I don't have a lot of specific experience with the Kinect sensor so I may be wrong, but I do have a lot of experience with IR tracking in general.

While most of the imaging chips found in most commercially available web cams do have the ability to track IR light the vast majority of the lenses in these devices have a filter in them that filters out this IR light.

Some of these filters are easy to remove some are not and some are impossible. The most common setup people are currently using is the Playstation 3 eye cam with a modified lens. But be careful some of the runs of that cam have a good easy to modify lens other don't check here for pictures http://nuigroup.com/forums/viewthread/5189/

You can also buy premodified versions of that camera and much better lens for IR tracking form here: http://peauproductions.com/store/index.php?main_page=index&cPath=1

As for the IR tracking itself, you are likely going to want to use one of the tracking systems already available and pass that information into Unity. Community Core Vision is currently one of the more popular trackers but there is also the older Touchlib and a couple others. I have used and contributed code to both Touchlib and CCV myself.

These trackers output the information in a format called TUIO and you can get that into unity with this plugin: https://code.google.com/p/unity3d-tuio/

In general you can find lots of great information and resources about IR tracking on the nui group forums. A lot of it is geared towards building homebrew large scale multitouch screens but you will still very likely find lots of usable information there.