This is a great keyboard, but made for PCs. I'm not sure if it's possible given that, but it would be great if the top row of keys (home, search, mail, favorites 1-5, calculator) as well as the middle scroll button and lower back/forward keys could be recognized by BTT.
BTW, I love BTT so much!!!
I'm looking into more generic USB support, however I currently don't have a timeline.
You could already use ControllerMate for this: http://www.orderedbytes.com/controllermate/compatibility/#microsoft/ergonomic_keyboard_4000