Falstar's DIY to cheap to buy the real NaturalPoint TrackClipPro thingyabob. This is a Work in Progress!
Step One:       Gather Parts and download the FreeTrack v.2.0 software.
In my "junk" box I had a IR Stereo transmitter, but no Wireless Headphones.  Unsolder IR leds.
USB Cable cut off of an old USB mouse.
For the HeadSet Clip I'll use one of these.
Bought them at the Auto Parts Store.
Have seen them at Walmart, etc. 
Clips around the headset just like theirs'.
Theirs: IR4 $180.00
          Clip  $39.99 
Radio Shack perf. circuit board.  # 276-150
47 mm x 72 mm        ( 1 7/8" x 2 7/8" )
(May have to find a bigger board in the future.)  Depends how it works out.
Step Two:  Prepare IR led lights
Mine: FreeTrack v.2.0  -FREE

HeadPhones - Borrowed/Stolen from my son.

IR leds - Junk box

USB cable - Old crappie USB mouse.

3 187 ohm Resistors, because that's what I had in the junk box.

Radio Shack perf board.
$1.99

Sunglasses Visor Clip - 2@ $2.99

About a 1.5 inch machine screw with 3 nuts.  (I don't know what size. If I had went to the store I would have known)

GE EasyCam  5 years old
$19.98
Layed out the 3 IR leds and resistors in "Parallel" 

If you don't know what that means this project may just be a step beyond your skill level.  That's why soldering methods are not covered in this tutorial either.  Sorry.

Tried to get as close to the layout diamensions as shown in the FreeTrack Setup Screen.  (Adjust accordenly)
The "copper" side of the circuit board.

TEST:  Works     6 dof, baby!
Will cut out the blackened out area since the middle IR led is being blocked
Links:
Board Layout in millimeters.
Legal:

Build at your own risk.
Not affilated with NP or the FreeTrack guys.
Logos used without their knowledge , but this is a hobby site.


Good Luck.
Step Three:   Prepare Clip
Removed Spring Wire Clip from the back.
Trimmed off the plastic tab that held the wire apart so the backside fits against your head.

Drilled hole for machine screw all of the way through the foam.

While I was doing this the little hinge pin fell out so will have to glue it back in.  But probably easier to remove the pin before drilling so you don't lose it.
Contact Info:
Email: falstar@gmail.com
Mounted IR HeadTracker Circuit board to machine screw with a jam nut.  Will have to look around for some of those nylon lock nuts.
Flipped around for RIGHT HEADSET Mounting
And flipped back around for LEFT HEADSET Mounting to headphones.

May, or may not wrap it in black electrical tape.   Don't know yet.