So Apple recently published a technote on how to use an external Bluetooth 4.0 usb module with OS X / Xcode / Simulator for doing BLE hardware and iOS software development. Unfortunately Bill and I have (had?) been unable to find any suitable BLE 4.0 usb modules that would work. IIRC, Bill tried TI, Nordic, and Broadcom (which you would think would work as that's what Apple appears to be using inside the latest Mac computer updates), with no joy.  
 
Long story short, a friend of mine at Apple put me onto the 1 (maybe 2) usb modules that have been shown to work. The first is from Buffalo (model # BSHSBD08BK) and the second is from CSR (part of their µEnergy BLE dev kit). The information about the CSR module is not concrete, as there has only been 3rd hand evidence of it working. I ordered several Buffalo modules from Amazon Japan, and should have them here in a few days. Plan is to have Bill write up a short post on how to get everything running smoothly. 
 
iBUFFALO Bluetooth4.0+EDR/LE USB (BSHSBD08BK)