Configure 1 of 2 keyboards for Dvorak
I type Dvorak myself. 

While I am interested in your idea, I do not believe that it is possible.

Matias makes a keyboard that is dedicated to Dvorak in hardware, for US $100. In other words it types in Dvorak when the Mac's software keyboard layout is set to U. S. You could purchase one of those.



From the company's description:


  Hardwired Dvorak layout. The Matias Dvorak Keyboard gives you the
  Dvorak layout, hardwired right into the keyboard. This approach has
  advantages that software-based solutions can’t offer.
  
  Software Dvorak layouts may not take effect until after you log in, so
  if you need to type a password, you’re stuck typing it in QWERTY. With
  the Matias Dvorak Keyboard, you’ll never have this problem.
  
  Switchable to QWERTY on the fly. A layout selection key lets you
  instantly &amp; easily switch the layout to standard QWERTY and back, for
  those times when non-Dvorak typists want to use the computer.
  
  The keyboard is labelled with both Dvorak and QWERTY key legends, so
  you can easily see which key is which.


I have not tried this model of keyboard, but I have used other Matias products.

I type in Dvorak using a standard QWERTY keyboard, setting the Mac OS and Windows to use a software Dvorak keyboard layout. The whole point of using Dvorak is to learn to type faster, and that should also include training yourself to type without looking at the keys on the keyboard. Therefore it makes no difference to me what is printed on the keycaps, as I never look at them. So any standard keyboard will work fine for me and I can do Dvorak mapping in software on Mac OS X, Windows, and Linux for that matter. 

Should it be necessary to toggle between Dvorak and the standard US QWERTY layout, that can easily be done in Mac OS X by assigning a keyboard shortcut in the Language &amp; Text pane in System Preferences.