USB HID Interception/modification

I am a big fan of Teensy++, I use it every single day with this
project I modified to convert a PS/2 QWERTY keyboard to dvorak without
any computer configuration:

I need to be able to do this same thing with a USB keyboard, so I need
something to act as a USB host for a keyboard, I came across this
project which would work perfectly:

But I don't know whether:

  1. A Teensy++ will work as a USB host, in this case would I need two?
    (one to act as a host, another as a device, then communicate between
    them somehow?)
  2. This USB Shield will work with Teensy or Teensy++:
    I've seen this page here:
    USB Host Shield Library, For Connecing Other USB Devices
    For the smaller 3.3V version, but to run with the Teensy it requires
    soldering (which I am not good at) and conversion to 3.3V when I'd
    like to keep it at 5, if I got the full-size version above, could I
    keep it at 5?
  3. Or is there a better option? Like the one hinted at here: Arduino Forum which would allow me not to even mess with a USB host or device, and just modify information on-the-wire. Obviously this would be best if possible.

I also don't mind buying some type of Arduino either, but I read that the UNO that the above project uses requires special drivers under windows and won't work in 'boot mode' (like the BIOS), which the Teensy will, and I need that functionality.

If I can get this working as expected, I'll post all the schematics
and source code to do so and probably buy and build more, one for each
of my computers and one to carry around.

Thanks for any help you can give me